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Symptom

E-mails can be received by POP3 and IMAP with the existing login credentials, but when you try to send an e-mail, the mail software warns that the mail server cannot be reached or does not respond.

Cause

There can be several reasons why the smtp server cannot be reached.

• Port 25 of your computer or router is blocked. Most ofen antivirus-software or routers block the port. Maybe you recently installed a new antivirus-software or a new router in your network? Antivirus-software prevents worms from sending mass e-mails over your smtp server. Some Speedport-routers by Telekom feature a „list of secure e-mail servers“ in their „Internet“ menu. Smtp servers not listed cannot be addressed.
• In your mail configuration the option „smtp server requires authentication“ is not checked.
• In your mail configuration you have opted for an encrypted connection, but do not have an SSL certificate for your domain.

Solution

In your antivirus-software allow your mail program to send mails through port 25 (some antivirus software do not offer this option, but in that case they also do not block the port).

Your router may contain a security setting, with which you can determine which smtp servers can be addressed. Add the mail server that you want to use to the list of secure servers or turn off the filter in general.

In your mail configuration check the „smtp server requires authentication“ checkbox. Use the same credentials that you use for the pop3 server.

Neither use password-, nor connection-encryption in your mail software.

Overview of frequently asked questions