Prolateral Consulting Ltd
Prolateral Consulting Ltd
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Prolateral offers primary and backup domain (DNS) services, with servers in key geographic locations providing the best service possible.


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


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.

Summary of server details

Outgoing server

As provided in your signup email.

Outgoing server protocol


Outgoing server port

25, 465, 587, 2525 or 8025

Authentication Type

Basic Authentication, SSL and TLS supported


As provided


As provided


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