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


TCP port 25 for SMTP (Simple Mail Transfer Protocol) is frequently blocked by Internet Service Providers (ISPs).  This is typically done to help prevent spam from with in their networks. 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 other SMTP servers, such MX Tools SMTP Servers.

To resolve this issue with MX Outbound we have provided alternative port to use for SMTP email.

Summary of server details

Outgoing server

As provided.
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Outgoing server protocol


Outgoing server port

25, 465, 587, 2525, 8025 or 10025

Authentication Type

Basic Authentication


As provided


As provided