What Is CGNAT?

• Understanding CGNAT

  CGNAT stands for Carrier-Grade Network Address Translation. It’s a technology some Internet Service Providers (ISPs) use to share a single public IP address between multiple customers.

  Because IPv4 addresses are limited worldwide, CGNAT helps ISPs make efficient use of the remaining address space. It works by routing many customers through the same public IP address when they access the internet.

  Why It Matters When Sending or Receiving Mail

  If you try to access your mail and receive an error saying that your IP address is blacklisted, or you are not able to access the mail server, it may be related to CGNAT.

  When multiple customers share the same public IP under CGNAT, one user’s activity (for example, sending spam or being compromised) can cause that IP address to be blacklisted. This affects everyone using that shared IP - even if their own connection is clean.

  Important: This Is Not an Mweb Issue

  If you’re connecting to Mweb’s mail servers from another network (for example, mobile data, office WiFi, or another ISP), your connection may pass through a CGNAT IP that has been blacklisted.
  In these cases, the problem lies with the network you’re connecting from, not Mweb’s mail servers.

  You can try the following:

  1. Switch networks (for example, connect through your Mweb connection instead of mobile data).

  2. Restart your router or toggle mobile data off and on to get a new IP.

  3. Contact your current ISP to report that their IP address is blacklisted.

  In Summary

  CGNAT is used by some ISPs to share public IP addresses between customers. If you are not able to access your email server because of a blacklisted IP, it’s caused by the network you’re connected to, not Mweb’s mail servers. Switching connections or contacting that ISP should resolve the issue.