Unable to Configure SMTP Successfully

[DannyJCG]

I'm trying to set up email alerts from our UPS (APC Smart-UPS SRT 2200RMXLI) and I am in:

Configuration > Notification > E-Mail > Recipients

I have the following settings:

Generation

Enable - Yes

To Address - *******@*******.co.uk

Format - Long

Server - Custom

Custom E-mail Server Settings

From Address - *******@*******.co.uk

SMTP Server - smtp.office365.com

Port - 465

Authentication Enable - Yes

User Name - *******@*******.co.uk

Password - ***************

Confirm Password - ***************

Advanced

Use SSL / TLS - Always

Require CA Root Certificate - No

When I test the connection I get an error:

Last Test Result (*******@*******.co.uk) Test e-mail failed; SMTP configuration error.

I have tried this with multiple settings, changing the port from 587 to 465, changing the email addresses, SLT settings. I can't get it to send the email.

Are there any known settings I need to be aware of? Is anyone else experiencing this same issue?