Skip to main content

Connection problems with local mail clients

Customers can configure local e-mail clients such as Mozilla Thunderbird or Microsoft Outlook to access their accounts and messages. Sometimes, there are connection problems, for which there may be different reasons. However, in our experience, there are two in particular that stand out:

1. Pre-configured routers

Many internet providers bundle their products with pre-configured routers, which are sent out to new customers who then install the devices in their homes or offices. Some of these have a setting enabled by default that is called “Secure Mail Servers” (or similar), for instance all such devices supplied by Telekom Deutschland. The setting enables the strict filtering of outgoing e-mail communication by server – however, the list of allowed servers is usually missing an entry for the SMTP of This may then result in connections to the relevant ports of our mail server to be refused when users attempt to send e-mails through their account. There are two ways to solve this problem: Either, add “” to the list of allowed servers, or deactivate this setting altogether.

2. Security Suites / Anti-Virus Software

Various popular Anti-Virus- and Computer-Security-Suite programs feature a dedicated “E-mail security” option which may block server ports that are essential for the sending and receiving of e-mail to and from If this happens, the only thing users can currently do to fix the issue is to deactivate the additional feature in their security software. In order to facilitate a permanent solution, we are actively working with the relevant software manufacturers to make sure will be added to their respective server whitelists in the future.