SMTP authentication error with base 64 encoding

[naga475]

we are using Zabbix 6.0 LTS, trying configure media type email, getting login denied error, we checked with Wireshark what is sending to the server we found some issue with base64 encoding, we are using connection security None authentication username/password,

wire shark information:-

Simple Mail Transfer Protocol
Username/Password:
[Expert Info (Warning/Protocol): base64 decode failed or is not enabled (check SMTP preferences)]
[base64 decode failed or is not enabled (check SMTP preferences)]
[Severity level: Warning]
[Group: Protocol]

please provide any help to resolve this issue.