Hello,
I use the panel centos Web Panel and from here it my create my certificate let’s encryt so I have my files
Installing full chain to /etc/pki/tls/certs/myhostname.cert
Installing full chain to /etc/pki/tls/private/myhostname.key
Installing full chain to /etc/pki/tls/certs/myhostname.bundle
and my myhostname.bundle file is empty is it normal?
So I set up my main.cf postfix file:
smtpd_tls_key_file = /etc/pki/tls/private/myhostname.key
smtpd_tls_cert_file = /etc/pki/tls/certs/myhostname.cert
and I had a problem receiving emails with several errors, and I received no email.
I have rewrite the main.cf file and I record this:
smtpd_tls_key_file = /etc/pki/tls/private/myhostname.key
smtpd_tls_cert_file = /root/.acme.sh/cwp_certs/myhostname/fullchain.cer
it works I receive emails well now. I do not understand why I had to get the fullchain.cer I had not put the .bundle file instead? If yes it is empty this file 
sorry for my english I’m french
Thank you