What a nightmare

I've had a horrible evening!
It happened when I tried to delete the emails I didn't want. Instead of deleting them, it sent them again, and then kept re-sending them. And when they came in, they sorted themselves into date order so they were all mixed up with emails that I wanted to keep. Anyway in-between the 5-minute surges, I managed to keep clearing some away and eventually got the backlog down so that fewer and fewer were coming back. And eventually I managed to file off all the ones I wanted to keep so then it became easier to delete the rogue ones. I think it's now clean.
I discovered that a problem with duplicated messages can arise with Macs that use 10.2.8 or earlier, but mine's 10.4.8 so I don't think it can be the same problem. As you both said, it might be a problem with the server. I'm with Zen as well as it happens, and I've never had a problem before so I've never had to call them. Nice to know you can get through to somebody if you need to though.
I've no idea why it happened but it seems to be all right now ....
I feel exhausted. I'm going to bed.
Hope I've not missed anything on the forums.
Thanks both of you for your advice.

Edit: Still got a problem. Tried to shut down and Mail wouldn't let me. Can't Quit Mail either. I'm quitting though. I've had enough for one night....