In Hosted Email Security(HES) / Email Security (EMS), outbound mails are rejected by UCEPROTECT.
MTA Logs show return message similar to:
Remote Server returned '554 5.7.1 <domain that rejected the email> #5.7.1 smtp; 554 5.7.1 Service unavailable; Client host ] blocked using uceprotect.net Remote Server returned '554 5.0.0 <domain that rejected the email> #5.0.0 smtp; 550-XXX Anti Spam Engine has blocked this Email because the sender IP 550 Address is blocklisted.>' <email@address>: host <host that reject the email> error: said: 553 NET 18.104.22.168/24 is UCEPROTECT- listed host [x.x.x.x] said: 550-Blocklisted in dnsbl-3.uceprotect.net: 550-Your ISP AMAZON-02 - Amazon.comm Inc. US/AS16509 is UCEPROTECT-Level3 550-listed for hosting a total of xxxxx abusers. See: 550 http://www.uceprotect.net/rblcheck.php?ipr=x.x.x.x (in reply to RCPT TO command)
Based on the return message above, the email was rejected because UCEPROTECT blocked AWS ASN (A huge number of AWS IPs are blocklisted by UCEPROTECT). Trend Micro is actively working with AWS support to fix this issue, but this is out of our control.
Trend Micro is actively looking into reported issues where UCEPROTECT is blocklisting IP addresses that Trend Micro uses for sending out email messages on behalf of our customers. UCEPROTECT claims that this is an anti-spam measure and publicly suggests our customers change service provider if the issue is not resolved quickly.
Currently these blocking issues cannot be resolved permanently by Trend Micro because of the following reasons:
· The criteria for customer IP’s being placed on UCEPROTECT block lists are not publicly available and appear to be overly aggressive in nature (entire IP ranges can be blocked based on a single ‘suspicious’ IP).
· UCEPROTECT refuses to interact with vendors (including Trend Micro) to help assist in understanding the criteria behind the blocking whereas other more reputable blocklists will engage with customers so that customers can proactively correct behaviour.
· Unlike other reputable blocklists UCEPROTECT also charges a fee for delisting which Trend Micro recommends our customers NOT to pay. Paying the fee will not prevent UCEPROTECT from again blocking the same IP in 1 day, 1 week etc. leading to further blocklisting and payment requests in the future.
As always, Trend Micro takes necessary measures to avoid having our IPs identified as a spam source. At the same time, we are advising our customers and their email recipients to avoid using UCEPROTECT’s blocklist.
Actionable steps against UCEPROTECT ASN blocking:
1. Check the status of the IP on the site, UCEPROTECT Network - Spam Database Query.
2. Under Test, select ASN from the drop down list. Enter the ASN Value found from the MTA Logs. As an example, AS16509. Click Start Testing.
3. Let the recipient server know that the issue is with UCEPROTECT and that they should allow our IPs. Trend Micro server IP addresses can be found on the following articles under the Inbound Servers section:
4. Inform your affected recipient(s) to stop using UCEPROTECT if possible, because it blocks the entire AWS ASN (16509), which will accidentally injure the emails from HES/EMS and all other services hosted in AWS.
5. At least, inform your affected recipients(s) to disable UCEPROTECT Level 3 check because Level 3 is overly aggressive and will cause collateral damages.
HES Related Articles:
· Frequently Asked Questions (FAQs) KB articles: