mail delivery system error mailer daemon

i have used the same emails from my contact list for the last year but suddenly when i send messages i received the following message in my junk mail

this is driving me crazy as i need to send messages

The following message to <************************> was undeliverable.
The reason for the problem:
5.1.0 - Unknown address error 550-'Requested action not taken: mailbox unavailable'

i am not very computer literate but i know that i havent altered anything but would appreciate any help


Question Info

Last updated October 28, 2018 Views 720 Applies to:

Click this link to resolve the issue:

Mark as Answer if its worked. Thanks.

Did this solve your problem?

Sorry this didn't help.

Great! Thanks for marking this as the answer.

How satisfied are you with this reply?

Thanks for your feedback, it helps us improve the site.

How satisfied are you with this response?

Thanks for your feedback.