Hello @RichE, welcome to the Let's Encrypt community. 
Here is the chain I presently see being served
$ openssl s_client -showcerts -servername mail.nova-security.co.uk -connect mail.nova-security.co.uk:443 < /dev/null
CONNECTED(00000003)
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 = mail.nova-security.co.uk
verify return:1
---
Certificate chain
0 s:CN = mail.nova-security.co.uk
i:C = US, O = Let's Encrypt, CN = R3
a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256
v:NotBefore: Nov 20 11:37:33 2023 GMT; NotAfter: Feb 18 11:37:32 2024 GMT
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
1 s:C = US, O = Let's Encrypt, CN = R3
i:C = US, O = Internet Security Research Group, CN = ISRG Root X1
a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256
v:NotBefore: Sep 4 00:00:00 2020 GMT; NotAfter: Sep 15 16:00:00 2025 GMT
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
---
Server certificate
subject=CN = mail.nova-security.co.uk
issuer=C = US, O = Let's Encrypt, CN = R3
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 3046 bytes and written 419 bytes
Verification: OK
---
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: F14A00006805A29AD11887D9292D0879D8F6A07E38B92B778157F90C5888C7EF
Session-ID-ctx:
Master-Key: 4289A32A28C42628465F6224B62CE5332AED9C08801BE0A742D752EE7A5714FAD00283F9A3BBB28E5B5D0A109E583EA3
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1700503790
Timeout : 7200 (sec)
Verify return code: 0 (ok)
Extended master secret: yes
---
DONE