When I try to add my 123 Reg (work) email to my phone it first finds my email address, and tells me it is not a trusted format. I click to continue, and then the error message reads: “Checking outgoing server settings failed!”
123 Reg is a hosting service, so the e-mail domain is presumably hosted by them. You don’t give details, but I’m supposing that the e-mail account is not youraccount@123-reg.co.uk, or whatever, but youraccount@yourdomain.something. In the past I’ve noticed that low-cost hosting often doesn’t provide proper certificates corresponding to the hosted domain, and that is likely to cause errors when using automatic configuration of accounts in e-mail apps.
If that is the case, apart from the obvious option of providing proper certificates, I think your best approach is to configure the account and identity manually. You’ll need to contact the administrator of your e-mail account to provide the IMAP and SMTP details. Those will typically look like:
IMAP server: imap.yourdomain.something
Port: 993
Security: SSL/TLS
I don’t recommend using POP on mobile devices.
SMTP (outgoing) server: smtp.yourdomain.something
Port: 465
Authentication method: Normal password
Connection security: SSL/TLS
It goes without saying that if the basic problem is indeed the server certificate, then you can expect an error when making the initial connection with a manual configuration. You’ll generally be offered the possibility of declaring a security exception so as to allow connection to a server that’s using a certificate that doesn’t correspond to your e-mail domain.