Answer by Daniele Santi for Telnet to Gmail SMTP server timeout

Those are gmail's MX servers, used to receive mail, and they accept connections to port 25 from here:

# telnet gmail-smtp-in.l.google.com smtpTrying 173.194.65.27...Connected to gmail-smtp-in.l.google.com.Escape character is '^]'.220 mx.google.com ESMTP b6si7271885eem.150 - gsmtp

While they technically are SMTP servers, they're not used to forward clients email, but only toaccept mail from other server to @gmail.com accounts.

To send mail with gmail use smtp.gmail.com, and yes, it responds on port 25 too:

# telnet smtp.gmail.com 25Trying 173.194.65.108...Connected to gmail-smtp-msa.l.google.com.Escape character is '^]'.220 mx.google.com ESMTP n1sm10228410eey.12 - gsmtp