The 501 error code primarily defines two problems (see attached picture for the exact error as seen under failed status). One is the destination or sender address is incorrect. This may be checked using the command prompt and telnet (see https://support.microsoft.com/kb/153119 for full details on how to do this). The other is the domain name was input into Crystal Management Console > Servers > ReportjobServer > (click on destination tab) CrystalEnterprise.Smtp with an @ at the beginning of the domain name, remove the @ to resolve the issue.
Legacy KB System (APS) Data: RESL207111 V1.0, Originally authored by MaTh on 01/12/2012, Last Edited by MaTh on 01/12/2012
Related ranges: SMS Add-on