Sometimes there is need to debug SMTP connection and there is no telnet which is usually used for that. There is solution for this problem.

You can use curl!

curl -v --connect-timeout 10 smtp://74.125.131.109:587/

will return

*   Trying 74.125.131.109...
* TCP_NODELAY set
* Connected to 74.125.131.109 (74.125.131.109) port 587 (#0)
< 220 smtp.gmail.com ESMTP b64sm140514ljf.82 - gsmtp
> EHLO MacBook-Pro-Boaa
< 250-smtp.gmail.com at your service, [151.80.137.178]
< 250-SIZE 35882577
< 250-8BITMIME
< 250-STARTTLS
< 250-ENHANCEDSTATUSCODES
< 250-PIPELINING
< 250-CHUNKING
< 250 SMTPUTF8
> HELP
< 214 2.0.0  https://www.google.com/search?btnI&q=RFC+5321 b64sm140514ljf.82 - gsmtp
214 2.0.0  https://www.google.com/search?btnI&q=RFC+5321 b64sm140514ljf.82 - gsmtp
* Connection #0 to host 74.125.131.109 left intact