Most likely email is incorrectly encoded, Mail.dll decodes properly encoded encoded-words.
string eml = @"subject: =?utf-8?q?Alarmfrom030024B6-HGHHvammurEfri?=
body";
IMail mail = new MailBuilder()
.CreateFromEml(Encoding.ASCII.GetBytes(eml));
Assert.AreEqual("Alarmfrom030024B6-HGHHvammurEfri", mail.Subject);
Can you attach raw eml version of the email headers?