I have already tried to post about this twice this morning but for some reason the post isn't appearing, it looks like the forum is broken for me. Anyway, I'll try and add to this post instead, it looks like exactly the same problem and I've also tried resetting my password. It also started just a couple of days ago for myself and for someone else I know who uses Virgin Media. GMail returns the error "TLS Negotiation failed, the certificate doesn't match the host., code: 550" when trying to connect to smtp.virginmedia.com.
When I connect using OpenSSL, it seems to have a problem with the certificate (Verification error: unable to verify the first certificate). Maybe that could shed more light on the problem? Also, if I check the certificate using an online checker it says "Intermediate certificate required. Unable to get issuer certificate".
openssl s_client -connect smtp.virginmedia.com:465
CONNECTED(00000003)
depth=0 CN = email.virginmedia.com
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 CN = email.virginmedia.com
verify error:num=21:unable to verify the first certificate
verify return:1
depth=0 CN = email.virginmedia.com
verify return:1
---
Certificate chain
0 s:CN = email.virginmedia.com
i:C = BE, O = GlobalSign nv-sa, CN = GlobalSign GCC R3 DV TLS CA 2020
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=CN = email.virginmedia.com
issuer=C = BE, O = GlobalSign nv-sa, CN = GlobalSign GCC R3 DV TLS CA 2020
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 2391 bytes and written 438 bytes
Verification error: unable to verify the first certificate
---
New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES256-GCM-SHA384
Session-ID: 8112C3A390D2B2DFAA9E0ED79D78DDE8CCCCBCFDA7F41E51DADD967071B5D2D0
Session-ID-ctx:
Master-Key: EFF3901FAEBA38C9B1026BBC878F428299D4B6B85551FD82F131098F989810F43297514A6264873F3DD3F3B6298798BE
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1668165585
Timeout : 7200 (sec)
Verify return code: 21 (unable to verify the first certificate)
Extended master secret: no
---
220 csmtp3.tb.ukmail.iss.as9143.net cmsmtp ESMTP server read
