Im trying to tcp connect yahoo's mail server on port 25 . I have 3 public ip addresses lets say:-

(all are allowed in SPF records)

How to telnet(or other checks) using particular ip addresses to yahoos mta (check if all three of my ip addresses are allowed to send email to yahoo)


According to the man page: -s sets the source IP address.

So you can do:

telnet -s yahoo_mail_server 25
  • for centos 6.7 with telnet-0.17-48.el6.x86_64. it has "-b" switch instead of "-s" – satch_boogie May 6 '17 at 16:43
nc -s -vz mta5.am0.yahoodns.net 25


telnet -b mta5.am0.yahoodns.net 25

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