Error code 501

[jedwardnolan]

Attempts to send emails (with @btinternet.com address ) result in  "Invalid mail address, must have a domain part Err.code 501". This has started to occur intermittently since about 2 weeks ago. Did a test with email sent to own address and problem still occurs.

Any help or suggestions appreciated.

[Tim_G]

Not helpful, I'm afraid, but it's just started happening to me as well. Including to e-mail accounts I've used many times in the past and replies to e-mails I've received.

The message "Invalid mail address, must have a domain part [Err code: 501]" is definitely not telling the truth.