Nope; see here Mail Server Certificate Expired and Is Not Utilizing Newest Generated Cert - #2 by Nummer378
and here Chain of Trust - Let's Encrypt has this text
Intermediate Certificates
Under normal circumstances, certificates issued by Let’s Encrypt will come from “R3”, an RSA intermediate. Currently, issuance from “E1”, an ECDSA intermediate, is possible only for ECDSA subscriber keys for allowlisted accounts. In the future, issuance from “E1” will be available for everyone.
Our other intermediates (“R4” and “E2”) are reserved for disaster recovery and will only be used should we lose the ability to issue with our primary intermediates. We do not use the X1, X2, X3, and X4 intermediates anymore.
IdenTrust has cross-signed our RSA intermediates for additional compatibility.
- Active
- Let’s Encrypt R3 (
RSA 2048, O = Let's Encrypt, CN = R3)- Signed by ISRG Root X1: der, pem, txt
- Cross-signed by IdenTrust: der, pem, txt (Retired)
- Let’s Encrypt R3 (
- Active, limited availability
- Let’s Encrypt E1 (
ECDSA P-384, O = Let's Encrypt, CN = E1)
- Let’s Encrypt E1 (