I agree with you, ruth_uk, that this problem started with the latest update (version 10.10.4 on a late 2011 MacBook Pro). I started having this problem when I made this update and even went to a store that sells Apple products (we don't have "Apple Stores" in México, just some that look like them, but can't use their name) to ask for help, 'cause I couldn't solve it for myself, and, after about half an hour, the guy that was helping me tried the "installing the account in another user" trick and, when we changed the outgoing server settings under my user account, it started working again (by that, I mean that I could send an e-mail using my internet provider outgoing server). The settings were the same we were using before, but then they started working fine.
To be more explicit, I'll send here a list of some problems I had (and I am having again) specifically with this account (gmail is working fine for now, but I just set up the account in Mail yesterday):
- the outgoing server port changed as it pleased (not anymore)
- on the list of outgoing mail server, my internet provider server is put automatically to Offline
- I also receive that error 1045 message
- and i can't send mails, just receive them.
I've done everything suggested here and nothing is working for me. That's why I set up my gmail account and now I'm starting to notify everyone that they must use my gmail account, not my internet provider's anymore. Or, when I need to send something, I choose the gmail outgoing server. But I really would like to have a solution to this problem, even if it has to come within another update.
Anyway, if anyone has another suggestion, I'm all ears!!! Thanks!