This keeps popping up - cannot verify this server: alreadingo.club

Go to Settings>Mail> and you'll find it there. just delete the aldingo server account. click it and a delete a button is there.

so how did you get that? it's a spam from pop up ads/sites that redirects you to calendar

What happens when you click the "Details" on the error popup message (See the Pic below)

Best would be to Delete and Add the email account that is creating the issue.

You may also try changing SSL settings

Settings > Password & Accounts > [Select the Mail account} > [Tape on Account with the email ID} > Advanced > SSL Settings > [Disable]

Click <Account (in Blue)

Click on DONE (in Blue) when exiting in the previous screen