Unable to log in to the mail client on iOS devices with the following error message:
CONFIG_TEXT: SSL certificate is not accepted
The certificate check via a command-line interface returns the following:
# openssl s_client -connect example.com:587 -showcerts -starttls smtp
depth=0 OU = Domain Control Validated, OU = Hosted by Internet Assist Ltd., OU = COMODO SSL, CN = example.com
verify error:num=10:certificate has expired
An SSL certificate on a domain has expired.
Renew an expired SSL certificate and try to log in to a mail client.