Alright so I just got BT Hub4 installed and for some reason the email was working with incoming and not working with outgoing SMTP, it took me 3 hours checking forums and reading replies, but most of them needed fiddling with router and verifying your domain or email with BT mail to get you going.
I didn’t do any of that cause it seemed inconvenient, everything was working fine before so it must be the router and the way it connects to my laptop, after exploring and testing I decided to download Mozilla Thunderbird and see what error am i going to get maybe it will be a bit more clear so i got this error “EHLO requires valid address Contact your mail administrator for assistance.“.
On MozillaZine it says 501 Syntax error in parameters or arguments
To cut long story short, I’ve changed my computer name to one name all small letters and no spaces, once you do that restart your Mac and try sending an email, everything should work fine, if it sorted then rename back your computer, it seems that BT Hub have a problem with spaces and they only check your computer name once.
If this solved your problem please let me know and share :)