Important Notice: Our web hosting provider recently started charging us for additional visits, which was unexpected. In response, we're seeking donations. Depending on the situation, we may explore different monetization options for our Community and Expert Contributors. It's crucial to provide more returns for their expertise and offer more Expert Validated Answers or AI Validated Answers. Learn more about our hosting issue here.

I keep getting “5.1.0 – Unknown address error 571-sorry, sender address has invalid format (#5.7.1 – chkuser)\” errors, especially from people with Blackberry devices. What can I do?

April 26, 2017address Error format invalid sender unknown

0

Posted

I keep getting “5.1.0 – Unknown address error 571-sorry, sender address has invalid format (#5.7.1 – chkuser)\” errors, especially from people with Blackberry devices. What can I do?

1 Answer

0

Posted

The sender is using an illegal character. In Blackberry’s case they’re using a spam firewall that uses the slash character (/) in the sending email address when messages are sent from the Blackberry device, regardless of the reply-to address. To work around this you can either recompile chkuser to allow for the illegal character, or turn off chkuser checks for their mail servers. Below is my tcp.