Issue: Outgoing SMTP connections using CRAM-MD5 authentication for pre-existing accounts is failing after upgrading to build 8517 from build 8496. CRAM-MD5 authentication works fine with POP3/IMAP for the same accounts and SMTP authentication using CRAM-MD5 works for newly created accounts. Clients affected are Apple iOS Mail, MacOS Mail, Mozilla Thunderbird and web applications such as WP-SMTP-Mail & Fluent SMTP.

Error: detailed SMTP logs in SmarterMail show the error "Exception: String reference not set to an instance of a String. Parameter name: s   at System.Text.Encoding.GetBytes(String s)   at MailService.TcpServerLib.SMTP.SMTPSession.CramMD5Validation(Domain domain, User user, String digest, String md5Hash)   at MailService.TcpServerLib.SMTP.SMTPSession.ProcessAuthData(String authData) rsp: 535 Authentication failed.

Work-Around: Changing authentication type in the client from "MD5 Challenge-Response" or "Encrypted Password" to "Password" or "Plain-Text" works around the issue for affected clients. Also using SmarterMail's "CHANGE PASSWORD" function and resaving the existing password immediately resolves the problem (although it would appear that SETTINGS > PASSWORD REQUIREMENTS > PREVENT PREVIOUS PASSWORD REUSE is also not working as this should be preventing changing the password to the same existing password).