Here are some of the most common reasons why messages are blocked and tips about how to improve the situation.
There are two ways that you can learn that you were blocked by ZEROSPAM
- You received an SMTP bounce, with an error message that might be cryptic if you are not versed in SMTP. Forward it to your mail administrator or use this page
- You received an email from ZEROSPAM saying that your mail was quarantined
Depending on which of these cases apply, here are common reasons for being blocked.
The recipient address is invalid
If the error code in your DSN (Delivery Status Notification) message says 550 User Unknown, it means you are trying to send your message to an invalid address. Check the address to make sure you had no typo. If you can’t detect one, call your intended recipient to validate that this address is correct.
Non FQDN HELO banner
If the error message in your DSN says something like Helo command rejected: need fully-qualified hostname, it means your message was sent from an email server, Exchange or other, that does not follow RFC5321 and identifies itself with something other than a valid domain name. This is often the case with automatically-generated messages such as messages sent by an application on your website. The solution is to modify the sending domain for these messages so that it complies with RFC standards. This must be done by your IT department or IT consultant. If you received this kind of error message after manually sending a regular business email from your own address, it indicates a serious sending server configuration problem on your end. Notify your IT department or IT consultant immediately as this will affect your ability to send email at large
If the error message in your DSN says something like Message rejected due to SPF fail - not authorized, it means the owner of the sending domain has published an SPF record to protect it from spoofing (find out more about SFP records here) and this message is being sent from a server not authorized in this SPF record. Your only option is to contact the domain owner and ask that the IP address of the sending server you are using be added to their SPF record. Otherwise, your messages will be rejected by all email servers performing SPF checks on incoming email. The URL included with the bounce message that starts ith openspf.org should help you sort everything out.
Greylisting is a spam detection technique based on a very simple principle: refusing every new sender’s first connection. It is incredibly efficient because many spamming softwares will not bother to retry a failed delivery whereas legitimate email servers will retry when they receive a temporary error message. Normally, you would not receive a DSN message if your message has been greylisted. Your sending server will simply retry and your second message will go through. But if you receive a DSN message with the word greylisting in it, it may mean that your server retries too fast (a minimum of 60 seconds should separate the first and second attempt). Sending that error message to your IT team so the server’s retry configuration can be modified is a good idea. You can also call your correspondent and ask them to whitelist your email address.
Message larger than 50 MB
50 MB is the maximum message size limit in our systems. If your message is larger than 50 MB, you will receive a notification message from ZEROSPAM that specifically states this is the reason for the rejection. You can try compressing the attachment or send the message through other means (through a file sharing service for instance).
Your email could also be blocked because you sending IP or domain is blacklisted, because an URL in your message points to a dangerous website, because the language you are using is similar to that used in a known spam campaign, or for a host of other reasons. Your best bet is to share this rejection message with your IT team or IT consultant to make sure they are aware of the situation and can take appropriate action. You can also call your correspondent to let them know you are currently unable to send email to them and they can troubleshoot this internally and/or with ZEROSPAM. If your email was rejected with a very low spam score or because of a banned file, you will receive a special interactive notification message from ZEROSPAM.
Message rejected with a low spam score
Your message may have just slightly exceeded the spam score limit used by ZEROSPAM. In the special notification message you will have received in such a case, there is a link that you can click to access a help request form. If you fill out this form and submit it, your request will be treated by our technical team within 24 hours. You will receive no reply but your email may be released based on the information you provided. You can also call your correspondent and ask them to whitelist your email address.
Message rejected because of a banned file
Your message may be rejected because of a banned attachment. Since executable files and Microsoft Office documents with infected macros are the main malware propagation vectors, all executable files, files that contain executable code, old versions (pre-2007) of Microsoft Office suite documents with macros in them are quarantined by ZEROSPAM. Your correspondent’s IT team may also have banned other types of attachments in their ZEROSPAM parameters. If the reason for rejection is a banned file, you will receive a special notification from ZEROSPAM specifically stating that reason. It contains a link that you can click to access a help request form. If you fill out this form and submit it, your request will be treated by our technical team within 24 hours. You will receive no reply and we will not release your email but we will inform your correspondent’s IT team so they can release your message from the quarantine if they so desire.