IP addresses and ports

If your corporate network blocks unknown IP addresses or port numbers, this page explains what you’ll need to configure in order for Mailosaur to work.


Some organisations operate security policies that deny outbound traffic by default. If your organisation does this, you’ll need to add Mailosaur’s services to your allowlist.

We may change to our IP addresses from time to time, and so we recommend allowing by domain name rather than IP address whereever possible.

Domains and IP addresses

Mailosaur is accessible via three primary IP addresses:, and

ServiceDomain nameIP address
SMTP (Legacy)mailosaur.io35.233.95.121
POP3 (Legacy)mailosaur.io35.233.95.121

Note that the Legacy SMTP & POP3 services only apply to customers connecting to in their test code.

Port numbers

For services to function, you must allow the following TCP ports:

ServicePort number(s)
Website, Dashboard, API443
SMTP25, 2525, 465 and 587
POP3110 and 995