Mail can’t send email from 123-reg accounts

Hi all,

I've got an issue with Mac Mail can’t send email from 123-reg accounts.

I know there is a lot of articles on simular matters and some I have tried out with no luck, others are just speaking a whole other language.

Any help would be greatly recived, here's my situation below:

Running a iMac 2.8GHz Intel Core i5 on OS X 10.8.3

I’m using 3 accounts on Macs Mail client, one is my iCloud account that is working fine and the other two are my 123-reg accounts that I use for business purposes. I’ve been working like this for a couple of years now and about 6 months ago I upgrade my operating system from Snow Leopard to Mountain Lion.

2 or 3 months ago I randomly got a problem where I was unable to send any emails from my 123-reg account, I could only receive emails. I checked my settings and they were all correct and unchanged so I attempted to delete them and recreate the account but with no such luck.

I then decided to check if it was a problem at 123-regs end and attempted to log into web mail. This worked and was able to both send and receive emails so eliminated that possibility.

I also have these accounts set up on my iPhone, so checked if there was any issues and everything was working fine. I then checked my iphone details and made sure the same was on my desktop and still no such luck.

I’ve tried out some of the articles I’ve found on here (the ones written in plain English) still no results. I’m not very IT illiterate and just wondered if anyone else has got any ideas, whether there is something specific with 123-reg accounts and Mac Mail?

Many thanks.