E-mail says it is sending but it isn’t received

I am running Outlook 2011 for Mac 14.3.2. It worked fine when I first installed. Then I started getting error messages. (Warning triangle in the corner) That was resolved by redoing account. Then e-mails with attachments wouldn't go through. They would leave the outbox and show up in the sent folder, but the recipients never receive. Then we ran Onyx. Some with attachments are now going through but some aren't and some even without attachments aren't. There is no rhyme or reason as to which ones go. There is no way to tell if it's gone. If it's important, I have to call the recipient to make sure it was received. About 10% aren't going through.

Also, it seems like we are getting a bunch of new spam type e-mails. May not be related.