[exim] Expired tls certificate

Hi all,

I'm finding that my tls certificate is expired:

openssl s_client -connect mail.diehlnet.com:25 -starttls smtp

depth=3 O = Digital Signature Trust Co., CN = DST Root CA X3
verify error:num=10:certificate has expired
notAfter=Sep 30 14:01:15 2021 GMT
CONNECTED(00000003)
......

Here is what I have in my /etc/exim.conf:

tls_certificate = /etc/letsencrypt/live/mail.diehlnet.com/fullchain.pem
tls_privatekey = /etc/letsencrypt/live/mail.diehlnet.com//privkey.pem

I have renewed the certificate from letsencrypt and the timestamp reflects that
fact. I've also restarted exim.

What am I missing?

Thanks in advance.

Mike