Email Spam Blocking

Working with the transactional emails service UniOne you may encounter instances of the system blocking the delivery of your emails, causing them to not reach their destination.

According to the company's anti-spam policy, UniOne provides automatic spam blocking. Perhaps sending from your account to some domains has been blocked.

General principles of spam blocking

  1. If user’s emails, sent from one UniOne server (SMTP), are rejected as spam by the recipient's server (eg, gmail,, etc.) for 10 times, the system will block the sending of messages from the current SMTP server, and then continue sending using other servers.
  2. If 5 UniOne servers are blocked for the particular domain, the system restricts sending to this domain and will no longer try to send emails to the recipients from this domain.

More information about spam blocking

Information about outgoing UniOne SMTP servers and recipient domains blocking can be obtained by a webhook (setting event “spam_block” : [“*”]).

The information will be returned as follows:

              "block_time":"YYYY-MM-DD HH:MM:SS",


block_time - outgoing SMTP blocking time (UTC)

block_type - can return one_smtp (if a single SMTP was blocked), all_smtp (if all SMTPs were blocked for the recipient’s domain)

domain - recipient’s domain name

SMTP_blocks_count - counter that shows the quantity of the blocked SMTP

domain_status - can return blocked or unblocked (shows whether the current domain is allowed to send to)

If you have a problem with sending to a particular domain and this domain is restricted but you are sure that the content you are sending is acceptable (not spam), feel free to contact the support to solve your problem.