What do these mean? (Mail Queue)

[evonet]

Hello,

I've been having this problem for the past week. I've scanned for viruses, checked redirects, but no problem.

Where do you think is the problem?

 

[Active8]

just click on the mail and see why it is frozen or not send

 

[johannes]

gmail? most likely mailbox full

 

[Richard G]

Or blocked due to spam, since I see the senders are various different domains.

 

[Dettol]

I think some people try to send spam via your server, block them better

 

[evonet]

Thanks for the information you provided.