Postfix and Dovecot still use old certificate

Hello all,

Although my certificate from Let’s encrypt is updated:
(Expiry date Mar 20 11:51:44 2019 GMT), Last successful renewal: 12/20/2018 2:51 PM,

Print screen from last request

when i try to manage my email on thunderbird or any other mail client I get a certificate warning for incoming and outgoing emails.

Current certificate: “This SSL certificate is already being used by : Webmin (domain.com), Usermin (host domain.com), Dovecot (host domain.com), Postfix”.
On thunderbird, if I check certificate status for imap it says:

Period of validity
Begins on: 26 June 2018
Expires on: 24 September 2018

This is strange because I had no issues for over a year

System information:

Webmin version: 1.900
Virtualmin version: 6.05
Ubuntu Linux: 16.04.3
Apache version: 2.4.18
Dovecot Server Version: 2.2.22
Postfix version: 3.1.0

Any advice or directions where to look are highly appreciated! Thank you.