the identity of "smtp.mobile.mail.yahoo.com"cannot be verified by mail

The easiest way to fix it is to delete the account, then add it back. Better yet, use the free Yahoo mail app.

You should never get that error with a major email provider like Yahoo. You certainly should NOT disable SSL or approve an invalid certificate, as that puts your email and your identity at risk. If you do get an error about an invalid certificate it is a misconfiguration of the mail account on your phone; provider like Yahoo simply do not let their certificates expire.

Contact Yahoo support team and ask them if that SMTP is correct (to my knowledge, it should be "smtp.mail.yahoo.com", but I don't use that provider, so you'd better investigate with their technicians).

Regards

Giulio

Have a read through this discussion particularly the post that talks about SSL.

Mail "cannot verify server identity" - Apple Community

I’ve seen this type of dialogue pop up while initially setting up an account and you usually have to manually approve the “indentity” to complete the setup process, may be something has triggered it later for you.

Note that SMTP is the Outgoing Server Settings, the solution from sunrisecat talks about the Incoming Server, so just be mindful of that. Also Port numbers are different depending on whether you select SSL or not, your Mail provider should be able to advise which to use.

Noted, suppose it’s because I still use pop that I wasn’t really thinking, but I was also just trying to highlight that the “mobile” part didn’t appear to form part of the SMTP address as pointed out by Proust.

Nice one, didn’t notice the “mobile” in the address, this might help the OP.

Read this to help you

http://pop2imap.com/yahoo_iphone.php

Those instructions are to set up a POP client. However, most users will want an IMAP client, so mail will sync with other devices and computers.