Incoming

Using telnet you can manually test if the destination server is correctly accepting the email. To do so, you have to lookup the destination route and try delivery:

# telnet destinationserver 25
Trying x.x.x.x...
Connected to destinationserver.
Escape character is '^]'.
220 destinationserver ESMTP
helo yourhostname.com
250 destinationserver at your service
mail from:<>
250 2.1.0 OK
rcpt to: user@domain.tld
250 2.1.5 OK
quit
221 2.0.0 closing connection
Connection closed by foreign host.
#

Please note that for the recipient callout we always use an empty “mail from:<>”

Outgoing

Using telnet you can manually test if a destination domain is correctly accepting the email. To do so, you have to lookup the destination MX record of the domain, and try a delivery:

# host destinationdomain
destinationdomain has address x.x.x.x
destinationdomain mail is handled by 10 destinationserver.
# telnet destinationserver 25
Trying x.x.x.x...
Connected to destinationserver.
Escape character is '^]'.
220 destinationserver ESMTP
helo yourhostname.com
250 destinationserver at your service
mail from:
250 2.1.0 OK
rcpt to: user@domain.tld
250 2.1.5 OK
quit
221 2.0.0 closing connection
Connection closed by foreign host.
#