Google "check email server using telnet" no quotes
Some of your output may vary but if you do not get any errors and you receive the email from the email server you can know that emial is flowing properly.
Also im not 100% sure if this answers your qestion however this is the way the check your email server form command line.
Also when using telnet be careful as 1 typo means you have start all over again.
From the port25 website
Here are all the commands I have bolded the command you will need to type out vs the output you will see.
telnet mail.port25.com 25
Connected to mail.port25.com (18.104.22.168).
Escape character is '^]'.
220 mail.port25.com (PowerMTA(TM) v4.0) ESMTP service ready
250-mail.port25.com says hello
MAIL FROM: <email@example.com>
250 2.1.0 MAIL ok
RCPT TO: <firstname.lastname@example.org>
250 2.1.5 <email@example.com> ok
354 send message
From: "John Smith" <firstname.lastname@example.org>
To: "Jane Doe" <email@example.com>
Subject: test message sent from manual telnet session
250 2.6.0 message received
221 2.0.0 mail.port25.com says goodbye