dovecot IMAP not working on iOS because of Let’s Encrypt certificate problem

So I was having an issue with the mail app in my iPhones not being able to get IMAP email from my dovecot server.
Turned out I needed to change my dovecot config from this:

ssl_key = </etc/dovecot/mail.{{ domain }}.key
ssl_cert = </etc/dovecot/mail.{{ domain }}.crt
ssl_ca = </etc/dovecot/mail.{{ domain }}.chain.pem

to this:

ssl_key = </etc/dovecot/mail.{{ domain }}.key
ssl_cert = </etc/dovecot/mail.{{ domain }}.chain.pem