(before sendmail restart)

SX3@makoto 22:24:29/210608(~)%  foreach i (587)
echo $i;  openssl x509 -text -noout -in <(openssl s_client -starttls smtp -connect imap4.z.example.com:$i ) |grep -A3 Valid
end  
587
depth=2 O = Digital Signature Trust Co., CN = DST Root CA X3
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = R3
verify return:1
depth=0 CN = imap4.example.com
verify return:1
250 HELP
DONE
        Validity
            Not Before: Mar 12 11:22:45 2021 GMT
            Not After : Jun 10 11:22:45 2021 GMT
        Subject: CN = imap4.example.com

sendmail restarted

SX3@makoto 22:24:38/210608(~)%  foreach i (587)
echo $i;  openssl x509 -text -noout -in <(openssl s_client -starttls smtp -connect imap4.z.example.com:$i ) |grep -A3 Valid
end
587
depth=2 C = US, O = Internet Security Research Group, CN = ISRG Root X1
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = R3
verify return:1
depth=0 CN = example.com
verify return:1
250 HELP
DONE
        Validity
            Not Before: Jun  8 11:44:05 2021 GMT
            Not After : Sep  6 11:44:05 2021 GMT
        Subject: CN = example.com

587 ports need -starttls smtp argument