[AC Question]

Gmail has decided to stop working for some of my "Other" / Personal (IMAP) accounts. I have a Samsung S5.
I am certain that it is a server setting issue, but when I go into Gmail settings I cannot access port and authentication settings - I'm pretty sure that I used to be able to set these. All that I can enter is a username, password and server. That's it!
I have tried deleting and re-adding the accounts but always get the same result. Gmail tells me "Certificate not valid - The security certificate for this email address isn't safe enough to use with Gmail."
If I could access the server settings I'm sure it would work.