Scrapy doesn't configure protocol versions explicitly when using ESMTPSenderFactory and neither does that class, so I would expect it to use global OpenSSL settings, including TLS 1.2 or 1.3 if supported. See https://twistedmatrix.com/documents/current/core/howto/ssl.html

Can you show the library versions printed by Scrapy?

It depends on the version of scrapy and which library version it uses for OpenSSL?
I use scrapy 2.0.1.
Scrapy prints the following when starting a job:
[scrapy.utils.log] Versions: lxml 4.5.0.0, libxml2 2.9.10, cssselect 1.1.0, parsel 1.5.2, w3lib 1.21.0, Twisted 19.10.0, Python 3.8.2 (default, Feb 26 2020, 15:09:34) - [GCC 8.3.0], pyOpenSSL 19.1.0 (OpenSSL 1.1.1d 10 Sep 2019), cryptography 2.8, Platform Linux-4.15.0-66-generic-x86_64-with-glibc2.2.5
Thanks for your help!

I suggest trying newer pyOpenSSL/cryptography/Twisted versions first.

I upgraded the versions to the newest:
cryptography==36.0.1 pyOpenSSL==22.0.0 twisted==21.7.0

Now I get a new error:
502 Server does not support secure communication via TLS / SSL

So it definitely looks like the issue is my mail server now. I will close this feature request.
Thank you for your quick help

Hi @wRAR I might still need your help.

The smtp server supports TLS1.2. I also tested this by creating a script with smtplib.
This script successfully sends my email using TLS1.2:

import smtplib, ssl

port = 587
smtp_server = 'smtp.office365.com'
sender_email = 'test1@test.com'
receiver_email = 'test2@test.com'
user = 'test3@test.de'
password = input('Type your password and press enter:')
message = 'test'

context = ssl.create_default_context()
context.minimum_version = ssl.TLSVersion.TLSv1_2
with smtplib.SMTP(smtp_server, port) as server:
    server.ehlo()  # Can be omitted
    server.starttls(context=context)
    server.ehlo()  # Can be omitted
    server.login(user, password)
    server.sendmail(sender_email, receiver_email, message)

I can't seem to get it to work with scrapy. I created a new scrapy project with a newer version(2.5.1) as well.
These are all my versions:
[scrapy.utils.log] INFO: Versions: lxml 4.7.1.0, libxml2 2.9.12, cssselect 1.1.0, parsel 1.6.0, w3lib 1.22.0, Twisted 21.7.0, Python 3.9.7 (default, Sep 3 2021, 12:37:55) - [Clang 12.0.5 (clang-1205.0.22.9)], pyOpenSSL 22.0.0 (OpenSSL 1.1.1m 14 Dec 2021), cryptography 36.0.1, Platform macOS-11.6.2-x86_64-i386-64bit

I still get the error:
[scrapy.mail] ERROR: Unable to send mail: To=['test@test.com'] Cc=[] Subject="tls-test" Attachs=0- 502 Server does not support secure communication via TLS / SSL

Do you have an idea what I could try next?

Are you using MAIL_TLS and port 587?

Both yes

I'll try to check this later

Hi @wRAR, sorry to bother you.
Do you have some more ideas of what I could try?

Actually "Server does not support secure communication via TLS / SSL" is a client error from Twisted and it's misleading because in fact it's the client that doesn't support STARTTLS.

Since Twisted 21.2.0 (twisted/twisted@abef121), ESMTPSenderFactory needs to be passed hostname to use STARTTLS. Unfortunately this isn't documented, but the whole of ESMTPSenderFactory isn't, the public interface seems to be sendmail() which we don't use.

The fix to this seems to be just passing hostname=self.smtphost to ESMTPSenderFactory() in MailSender._sendmail(), but only for Twisted 21.2.0 and above.