A telnet client is a handy testing tool for testing connectivity between servers. Today I needed to test an SMTP server connection from a linux environment so I wrote the following script. You could use the same technique manually to do the same thing as long as your have access to a telnet client.
The script takes three parameters: the smtp server url, the sender address and the recipient address.
#!/usr/bin/env bash (echo HELO sleep 10 echo MAIL FROM\:$2 sleep 10 echo RCPT TO\:$3 sleep 10 echo DATA sleep 10 echo . sleep 10 echo QUIT) | telnet $1 25