555 Syntax Error
From SuperbHosting.net Support Wiki
This document is intended for those operating their own mail servers or smarthosts and/or systems or software that send mail through automated or scripted means. Examples of this would be an office PBX system sending voicemails to its users via email or a crontab on a remote server sending a report to an email address where the email accounts are hosted on Superb's mail servers.
When sending mail through Superb's mail servers, you get a 555 syntax error (#5.5.4) error
This error can happen for a few reasons. It is usually generated as a result of a restriction placed on the mail servers to avoid receiving improperly formated (and possibly infected or spam) mail.
One reason for this, although unlikely, is because of the hostname your server is introducing itself has when sending the "HELO" or "EHLO" command to our mail server is incorrect. This problem may occur if the sending server is not in accordance with the RFC 821 and RFC 1869 documents. The receiving mail server expects either a host name only or a fully qualified domain name (FQDN) following the EHLO/HELO command. A trailing dot after the FQDN is interpreted as incorrect syntax, and a 5xx error message is generated. If the fix below does not provide a solution to this problem I'm afraid you may have to contact the vendor of the PBX/Voicemail system for information.
NOTE: A trailing space also generates this error message. I do not see either a trailing dot or a trailing space in the capture you have sent though.
The other reason for this, which is more common, is the restriction that an email must have a valid "FROM" address when setting up the session with our server. Without a valid "FROM" address the email is not RFC compliant and most mail servers will not accept mail under these circumstances these days (some will, but most won't). This restriction is growing in popularity to avoid email being sent to and through mail servers that cannot be bounced.
Below is an example of what the mail server sees when setting up an ESMTP session incorrectly.
# telnet smtp2.superb.net 25 Trying 207.228.225.131... Connected to smtp2.superb.net. Escape character is '^]'. 220 smtp2.superb.net ESMTP helo superb.net 250 smtp2.superb.net MAIL From: <> 250 ok RCPT To: username@hosteddomain.com 555 syntax error (#5.5.4) quit 221 smtp2.superb.net Connection closed by foreign host.
Below is the same test with an address in the MAIL From: command.
# telnet smtp2.superb.net 25 Trying 207.228.225.131... Connected to smtp2.superb.net. Escape character is '^]'. 220 smtp2.superb.net ESMTP helo superb.net 250 smtp2.superb.net MAIL From: address@somedomain.com 250 ok RCPT To: username@hosteddomain.com 250 ok quit 221 smtp2.superb.net Connection closed by foreign host.
If the email is being sent from software that you cannot control the FROM address you must contact the vendor. Otherwise, please check the settings of the software in question and ensure the FROM address is set.
