Mail 3.3 won't send attachments

Question

Ever since upgrading to Leopard 10.5.4 I haven't been able to send attachments over about 30Kb. I have dialup with NetZero and have checked all of the modem and Network settings. I've been using this same dialup for 5 yrs or so and have never had a problem with previous OS's. The last was 10.4.11. When I attempt to send an attachment of over 30Kb, Mail will spin for 5 min. or so and finally generate the following: "Cannot send message using the server smtp.netzero.com". I checked with NetZero and that is the correct address for their outgoing mail server.To check that I didn't have some other problem I tried FTPing a file via an FTP client and that worked fine.
I did try sending an attachment using the browser based email program from NetZero and had a similar problem...I'm using Safari 3.1.2 for that BTW. In NetZero it spun it's wheel for a few minutes and simply didn't load the attachment. This leads me to think that this is more of an OS issue in that it does the same thing with 2 different programs.
Anyone have any thoughts? Thanks in advance.

Answer 1

I'm having similar trouble with Mail 3.3 after upgrading to Leopard despite years of trouble-free use with exactly the same set up on previous OSs and versions of Mail.
It boils down to frequent but erratic SMPT errors - sometimes the mail goes, sometimes it doesn't. I've found that clicking the Connection Doctor button sometimes helps. But sometimes it doesn't.
Sometimes it's only emails with attachments that get snagged, other times it's all emails.
Why does something that used to work fine have to get worse with an upgraded version? iPhoto seems to have got worse too (no dragging to folders from full-screen view). Come on, Apple, sort it out or we'll all have to abandon your Apps.