Problem

Port 25 Blocking?
Cannot send emails on SMTP Port25, why?

Solution

TCP port 25 for SMTP (Simple Mail Transfer Protocol) is frequently blocked by Internet Service Providers (ISPs), as an anti-spam technique. Some Internet providers have recently started blocking port 25 in an attempt to help prevent direct to MX spamming, and abuse of open proxies or relays from their dialup and/or broadband customers.

Port 25 is the default port used by SMTP, and blocking it prevents users from connecting to arbitrary email servers and sending email. Unfortunately a side-effect of this practice is that it prevents users from accessing our SMTP servers (outMail).

To resolve this issue with outMail instead of sending your outbound SMTP messages using port 25, try an alternative port support by outMail. The ports supported by outMail are 25, 587, 2525 and 8025.