My Mdaemon rejects maisend-go sent mails.

[nauete]

Hi, I have a Mdaemon server and one of my customers is trying to send e-mails to his customers using mailsend-go, but I get this everytime:

Thu 2022-09-15 10:38:04: Accepting SMTP connection from [xxxxxxxxxxxxxxxxxxxxxxxxxxx] to [xxxxxxxxxxxxxxxxxxxxxxxxxxx]
Thu 2022-09-15 10:38:04: --> 220 xxxxxxxxxxxxxxxxxxxxxxxxxxx ESMTP MSA MDaemon 13.5.1; Thu, 15 Sep 2022 10:38:04 +0200
Thu 2022-09-15 10:38:04: <-- EHLO localhost
Thu 2022-09-15 10:38:04: --> 250-xxxxxxxxxxxxxxxxxxxxxxxxxxx Hello localhost, pleased to meet you
Thu 2022-09-15 10:38:04: --> 250-AUTH LOGIN CRAM-MD5 PLAIN
Thu 2022-09-15 10:38:04: --> 250-8BITMIME
Thu 2022-09-15 10:38:04: --> 250-STARTTLS
Thu 2022-09-15 10:38:04: --> 250 SIZE
Thu 2022-09-15 10:38:04: <-- STARTTLS
Thu 2022-09-15 10:38:04: --> 220 Begin TLS negotiation
Thu 2022-09-15 10:38:04: SSL negotiation successful (TLS 1.0, 256 bit key exchange, 256 bit encryption)
Thu 2022-09-15 10:38:04: <-- EHLO localhost
Thu 2022-09-15 10:38:04: --> 250-xxxxxxxxxxxxxxxxxxxxxxxxxxx.com Hello localhost, pleased to meet you
Thu 2022-09-15 10:38:04: --> 250-AUTH LOGIN CRAM-MD5 PLAIN
Thu 2022-09-15 10:38:04: --> 250-8BITMIME
Thu 2022-09-15 10:38:04: --> 250 SIZE
Thu 2022-09-15 10:38:04: <-- AUTH CRAM-MD5
Thu 2022-09-15 10:38:04: --> 334 PE1EQUVNT04tRjIwMjIwOTE1MTAzOC5BQTM4MDQ3ODFNRDAwMTJAbWFpbC5uZmluaXRlOTAwMC5jb20+
Thu 2022-09-15 10:38:04: <-- bm9yZXBsYXktbGFtYWdyYW5hQGxhbWFncmFuYXZhbGxlc2FuYS5jYXQgNTg1MjIxOTA0ZjUyMTVhNzIwODUyNzA5NDJhZGE0Nzg=
Thu 2022-09-15 10:38:04: --> 235 Authentication successful
Thu 2022-09-15 10:38:04: Authenticated as xxxxxxxxxxxxxxxxxxxxxxxxxxx
Thu 2022-09-15 10:38:04: <-- MAIL FROM: BODY=8BITMIME
Thu 2022-09-15 10:38:04: --> 250 , Sender ok
Thu 2022-09-15 10:38:04: <-- RCPT TO:
Thu 2022-09-15 10:38:04: --> 250 , Recipient ok
Thu 2022-09-15 10:38:04: <-- DATA
Thu 2022-09-15 10:38:04: Creating temp file (SMTP): c:\mdaemon\queues\temp\md50000047311.tmp
Thu 2022-09-15 10:38:04: --> 354 Enter mail, end with .
Thu 2022-09-15 10:38:04: Message size: 478 bytes
Thu 2022-09-15 10:38:04: Passing message through AntiVirus (Size: 478)...
Thu 2022-09-15 10:38:04: * Message is clean (no viruses found)
Thu 2022-09-15 10:38:04: ---- End AntiVirus results
Thu 2022-09-15 10:38:04: Socket error sending response to DATA
Thu 2022-09-15 10:38:04: * Winsock Error 10054
Thu 2022-09-15 10:38:04: SMTP session terminated (Bytes in/out: 1625/4983)

He was using mailsend old version and worked perfectly, but now he needs to use html templates and attaching files / images and switched to mailsend-go.

Can you help?Thanks.