If you have already been testing the Telnet’s GMAIL SMTP, you must have seen the following error:
530 5.7.0 Must issue a STARTTLS command first. - gsmtp
This means that you have didn’t encrypt the connection first. This is quite easy to fix by following the steps below.
Step 1. Run the following command:
openssl s_client -starttls smtp -ign_eof -crlf -connect <some_mail.server>:587
-ign_eof: Ignores EOF.
-clrf: Relates to the control characters CR (Carriage Return) and LF (Line Feed).
Step 2. To use port 465 instead of 587, run:
openssl s_client -connect <some_mail.server>:465
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