Given an email address is it possible to determine what the smtp address is using python. I am building an email application using python smtplib.
Thanks
The Python smtplib module does not perform mail routing, so it leaves that to a smart host.
You could use dnspython to look up MX records for the destination domain (and A and AAAA records if there is no MX record). The resulting address you can then pass to smtplib.
However, this is only a small fraction of the work that is needed to implement proper mail routing: If the target mail server is unreachable or times out, you are supposed to try the next server. Similarly if it responds with a 4xx error code. If all servers are unavailable, you need to temporarily store the message locally, so you need to implement your own mail queue. Furthermore, your external IP address may be blacklisted for mail delivery.
Therefore, it is usually easier to install a local mail server such as Exim or Postfix and use that to inject mail, possibly routing it via a smart host with good email reputation to avoid blacklisting.
Disclaimer: I hesitated on the title, due to the broad nature of this question (see below), other options included:
How to send a mail from localhost, using Python code only?
How to send email from Python code, without usage of external SMTP server?
Is it possible to send an email DIRECTLY to it's destination, using localhost and Python only?
First, a little bit of context:
For the sake of learning I am building a website with user registration feature. The idea is that after registration user will receive an email with activation link. I would like to compose & send email from Python code, and that is the part where I would like to ask for some clarifications.
My understanding, before I began (obviously naive =) can be illustrated like this (given that there is a legitimate email address user#example.com):
After searching for examples, I bumped into some questions & answers on stackoverflow (1, 2, 3, 4). From these I've distilled the following snippet, to compose and send an email from Python code:
import smtplib
from email.message import EmailMessage
message = EmailMessage()
message.set_content('Message content here')
message['Subject'] = 'Your subject here'
message['From'] = 'me#example.com'
message['To'] = 'user#example.com'
smtp_server = smtplib.SMTP('smtp.server.address:587')
smtp_server.send_message(message)
smtp_server.quit()
Next (obvious) question was what to pass to smtplib.SMTP() instead of 'smtp.server.address:587'. From the comments to this answer, I discovered that local SMTP server (just for testing purposes though) could be started via python3 -m smtpd -c DebuggingServer -n localhost:1025, then smtp_server = smtplib.SMTP('smtp.server.address:587') could be changed to smtp_server = smtplib.SMTP('localhost:1025') and all the sent emails will be displayed in the console (from where python3 -m smtpd -c DebuggingServer -n localhost:1025 command was executed), being enough for testing — it was not what I wanted (my aim was — the ability to send a mail to 'real-world' email address from local machine, using Python code only).
So, the next step would be to setup a local SMTP server, capable of sending an email to external 'real-world' email-address (as I wanted to do it all from Python code, so the server itself would better be implemented in Python too). I recalled reading in some magazine (in early 2000), that spammers use local servers for sending mails (that particular article was talking about Sambar, development for which have ended in 2007, and which was not written in Python :-) I thought there should be some present-day solution with similar functionality. So I started searching, my hope was to find (on stackoverflow or elsewhere) a reasonably short code snippet, which will do what I wanted. I haven't found such a code snippet, but I came across a snippet titled (Python) Send Email without Mail Server (which uses chilkat API), though all I needed (supposedly) was right there, in the comments to code, the first line clearly stated:
Is it really possible to send email without connecting to a mail server? Not really.
and a few lines below:
Here's what happens inside those other components that claim to not need a mail server: The component does a DNS MX lookup using the intended recipient's email address to find the mail server (i.e. SMTP server) for that domain. It then connects to that server and delivers the email. You're still connecting to an SMTP server — just not YOUR server.
Reading that, made me understand — I, clearly, was lacking some details in my understanding (reflected on picture above) of the process. To correct this I have read the whole RFC on SMTP.
After reading the RFC, my improved understanding of the process, might be pictured like this:
From this understanding, came the actual questions I'd like to clarify:
Can my "improved understanding" be considered correct, as a general picture?
What addresses, exactly, are returned by MX lookup?
using host -t mx gmail.com command (suggested by this answer), I was able to retrieve the following:
gmail.com mail is handled by 10 alt1.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 20 alt2.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 40 alt4.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 30 alt3.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 5 gmail-smtp-in.l.google.com.
- but none of these are mentioned in the [official docs][13] (ones that are there: `smtp-relay.gmail.com`, `smtp.gmail.com`, `aspmx.l.google.com`)
Is authentication always needed to pass an email to SMTP-server of an established mail service (say gmail)?
I understand that to use, say smtp.gmail.com for mail submission, you'll need, regardless if the recipient has a #gmail address or not (as it stated in docs):
Your full Gmail or G Suite email address is required for authentication.
But, if an email to user#gmail.com is submitted to SMTP-server not owned by gmail, then it'll be redirected to one of the gmail servers (directly or via gateway/relay). In this case (I assume) sender of an email will only need to authenticate on mail submission, so after that gmail server will accept the mail without authentication?
If yes, what is preventing me from "pretending" to be such a gateway/relay and hand over emails directly to their designated SMTPs? Then it, also should be pretty easy to write a "proxy-SMTP", which will just search for an appropriate server via MX lookup, and hand an email to it, sort of, directly.
Documentation on gmail SMTP, also mentions aspmx.l.google.com server, which does not require authentication, though:
Mail can only be sent to Gmail or G Suite users.
With that being said, I assume the following snippet should work, for submitting a mail to ExistingUser#gmail.com mailbox:
<!-- language: lang-python -->
import smtplib
from email.message import EmailMessage
message = EmailMessage()
message.set_content('Message test content')
message['Subject'] = 'Test mail!'
message['From'] = 'me#whatever.com'
message['To'] = 'ExistingUser#gmail.com'
smtp_server = smtplib.SMTP('aspmx.l.google.com:25')
smtp_server.send_message(message)
smtp_server.quit()
When ran, the code above (with ExistingUser#gmail.com replaced by the valid mail) throws OSError: [Errno 65] No route to host. All I want to confirm here is that the communication to aspmx.l.google.com is handled correctly in code.
Your understanding of how mail works is roughly correct. Some additional notes that may clear things up:
SMTP is used for two distinct purposes. You seem to be confusing these two.:
The first use, typically called "submission", is to send a mail from an MUA (Mail User Agent, your mail program, Outlook, Thunderbird, ...) to an MTA (Mail Transfer Agent, typically called "mail server"). MTAs are run by your ISP, or by mail-providers such as GMail. Typically, their use is restricted by either IP address (only customers of said ISP can use it), or username/password.
The second use is to send mail from one MTA to another MTA. This part is, usually, wide open, since you are probably willing to accept inbound mail from anyone. This is also the location where anti-spam measures are taken.
In order to send a mail, you need, at least, the second part of SMTP: the ability to talk to another MTA to deliver the mail.
The typical way to send mails is to compose the mail in your application, then send it off to an MTA mail server for delivery. Depending on your setup, that MTA can be either installed on the same machine as your Python code is running on (localhost), or can be a more "central" mail server (possibly requiring authentication).
"Your" MTA will take care of all the nasty details of delivering mail such as:
Doing DNS lookups to find out the MTA's to contact to relay the mail. This includes MX-lookup, but also other fallback mechanisms such as A-records.
Retrying delivery, if the first attempt fails temporarily
Generating a bounce message, if the message fails permanently
Make multiple copies of the message, in case of multiple recipients on different domains
Signing the message with DKIM to reduce the chance of it being marked as SPAM.
...
You could, of course, re-implement all these features within your own Python code, and effectively combine an MTA with your application, but I strongly advise against it. Mail is surprisingly hard to get right...
Bottom line: Try to send the mail via SMTP to the mail server of your provider or another mail service. If that is not possible: think really hard if you want to run your own mail server. Being marked as a spammer happens easily; getting removed from spam-lists is much harder. Don't re-implement SMTP-code in your application.
Thanks to these answers, to my additional questions: 1, 2, 3, as well as these two questions (and answers) of other people: one, two — I think I am now ready to answer the questions I have posted, on my own.
I will address the questions one by one:
Yes, as a general picture, sending of an email can be portrayed like this:
MX lookup returns address(es) of server(s) which receive email destined to the specified domain.
As to "Why smtp-relay.gmail.com, smtp.gmail.com, aspmx.l.google.com are not returned by host -t mx gmail.com command?". This point is, pretty much, covered in another answer to this question. The main points to grasp here are:
servers returned by MX lookup are responsible for receiving of emails for the domain (gmail, in this particular case)
servers listed in gmail docs are meant for the mail sending (i.e. mails that gmail user wants to send, to other gmail user or otherwise, are submitted to those servers)
Authentication is not needed, for servers receiving emails (i.e. the ones returned by MX lookup).
There are a couple things that prevent such servers from being abused:
many ISPs block outbound connections to port 25 (which is default port for mail receiving servers), to prevent such "direct" mail sending
there are numerous measures taken on the side of receiving servers, which are, mainly, intended to prevent spamming, but as a result will, likely, prevent such "direct" mail sending, as well (some examples are: DNSBL — list of blocked IPs, DKIM — is an email authentication method designed to detect forged sender addresses in emails (if you do not have your own, legitimate, mail server, you will use someone other's domain for From field, that is where you might be hit by DKIM)
Code snippet is OK. The error is produced, in all probability, due to the blocking on the ISP's side.
With all that being said, code snippet:
import smtplib
from email.message import EmailMessage
message = EmailMessage()
message.set_content('Message content here')
message['Subject'] = 'Your subject here'
message['From'] = 'me#example.com'
message['To'] = 'user#example.com'
smtp_server = smtplib.SMTP('smtp.server.address:25')
smtp_server.send_message(message)
smtp_server.quit()
will actually send an email (see this question, for real-world, working example) given that smtp.server.address:25 is legitimate server and there are no blockings on ISP's and/or smtp.server.address side.
I have a pretty basic networking assignment where I have to make a manual SMTP request (with the HELO, MAIL FROM:, and the like) as the client to the SMTP server in order to send an email.
It doesn't seem like you can do this anymore with Gmail, as it requires an encrypted SMTP request for obvious reasons.
I know I can do this with OpenSSL, but this is to be build with Python and it seems like an external library would have to be used for this, which isn't allowed on the assignment.
So if possible I'd like to be able to submit this unencrypted for simplicity's sake. Are there any test servers to send non-encrypted SMTP over now a days?
Inbox.py is here to save you (made by the author of python-requests: Kenneth Reitz), it's a very simple SMTP server "made for Humans".
Useful for your test purpose, I think.
I'm building a application that needs to send and receive emails.
However I do not want to have a separate email server (or use IMAP and POP3), since I need to create/delete/manage inboxes on the fly, with no email inbox passwords, etc.
I have an email storage database in place, and I can receive emails by using a custom smtpd server, replacing postfix. However, that way I'm not able to send emails via postfix (using smtplib, connecting through port 25 to postfix and sending emails)
Any solution to this problem? How to send emails with a custom smtp server? Can I configure postfix to relay all incoming emails to a custom smtp server running in another port, and still use postfix on port 25 to send emails?
Thanks for your time
By using a custom SMTP server, you run the risk of inadvertently creating security holes or violating the SMTP protocol in some way. With so many great SMTP servers out there (Postfix, exim, sendmail...), that doesn't sound like a good option to me.
The easiest way I can think of to solve that issue is to use Postfix to relay inbound and outbound e-mail.
Inbound e-mail can be configured to be piped to an application, and outbound e-mail can be configured to be delivered by Postfix, either directly or relayed through a different server.
This way, you can use, instead of a custom SMTP server, an application that is able to parse RFC822-compliant message files. This is better than doing exactly the same thing, but with the overhead of having to implement the SMTP protocol.
This approach probably won't scale well should you need to receive a high volume of messages - every message will fork+exec a new process. If that is a requirement, a good approach would be to keep a custom SMTP server to do that job, but let Postfix relay it the messages - you will then benefit from Postfix's architecture in front of your parser.
Assuming you follow the approach of piping the messages to an application, all you need to do in Postfix is to
Configure Postfix's alias_maps' parameter to look for such a map:
alias_maps = hash:/etc/aliases, hash:/etc/postfix/app-aliases
Then, configure the map to pipe messages sent to each address into an application:
test: "|/usr/local/bin/your-app"
As usual, don't forget to $ postalias app-aliases.
This will make a message sent to test#yourdomain be piped into /usr/local/bin/your-app, which acts as an e-mail gateway to your application.
I am running a site where users can private message each other. As with any other such website, to read and mark their messages, users must log on to the site.
I wish to expose an IMAP interface so that users may read their site messages using their standard email client. There would be few complications in such approach as what be userid to email-address mapping and what would happen if the user replies a mail but for the time being I'm little concerned about these issues.
Is there any lightweight raw IMAP server in Python to which I could just add few rules or logic to expose an IMAP interface to user's messages?
Twisted Mail project:
Twisted Mail contains high-level, efficient protocol implementations for both clients and servers of SMTP, POP3, and IMAP4. Additionally, it contains an "out of the box" combination SMTP/POP3 virtual-hosting mail server. Also included is a read/write Maildir implementation and a basic Mail Exchange calculator (depends on Twisted Names).
The examples for IMAP4 contain only a client. Look into the source for more information.