Telnet - SMTP
To test a POP3 connection using telnet open a command window or shell terminal and type the following
telnet smtp.domain.com 25
Where smtp.domain.com is the FQDN (Fully Qualified Domain Name) or IP address of the server you wish to test.
25 also assumes default SMTP configuration.
You will be greeted with something similar to:
Escape character is '^]'. 220 smtp.domain.com
Now you need to enter the HELO command, followed by an idenfication of the server you ar esending from.
HELO buzz.domain.com 250 smtp.domain.com
Anything other than “250” indicates a problem.
You can now proceed with the test email transaction.