sent message undelivered bounced back now mail cannot receive/send messages

Hello i have got a problem with my mail account I atrempted to email a gallery with attachments, which they asked me to increase file sizes for quality issues but the attachment was 164 mg but when I sent email it tried to bounce back to me and was in drafts i then deleted it but it kept coming back at one point there was 7 of them. I tried changing the port and doing rebuild, none of which worked i was able to receive messages but now it is not receiving messages either. My ISP is sky and when I log into my sky account that seems ok its receiving messages fine but I prefer to use the safari mail on the mac.

The error message i am receiving is
Some actions taken while the account address was offline could not be completed online
Mail has undone actions on some messages so that you can redo the actions while online mail has saved other message in mailbox drafts in on my mac so you can complete the actions while online
the IMAP command APPEND (TO DRAFTS) failed with server error could not parse command.

and also had message that port 993 timed out

I am now totally confused and I am not sure whether I should be telephoning my ISP or not?

Sorry but I am fairly new to using the internet and later found out that the server cannot send receive more than 34 mg so i must of overloaded it and now don't know how to delete this message

Hoping someone can help or explain what I need to do.
Thanks