I would encourage you to use a library rather than deal with the -rather unpythonic- built-in mail modules, such as the highly recommended envelopes: https://tomekwojcik.github.io/envelopes/index.html install with: Python code:
EDIT: Super Redux Version Try port 587 instead of 465. Port 465 is technically deprecated. After a bunch of packet sniffing I figured it out. First, here’s the short answer: The .NET SmtpClient only supports encryption via STARTTLS. If the EnableSsl flag is set, the server must respond to EHLO with a STARTTLS, otherwise it will throw an exception. See … Read more
SMTP protocol: smtps (port 465) v. msa (port 587) Ports 465 and 587 are intended for email client to email server communication – sending out email using SMTP protocol. Port 465 is for smtpsSSL encryption is started automatically before any SMTP level communication. Port 587 is for msaIt is almost like standard SMTP port. MSA should accept email after authentication (e.g. after SMTP … Read more
From RFC 5321, section 2.3.11: The standard mailbox naming convention is defined to be “local-part@domain”; contemporary usage permits a much broader set of applications than simple “user names”. Consequently, and due to a long history of problems when intermediate hosts have attempted to optimize transport by modifying them, the local-part MUST be interpreted and assigned … Read more