It seems newsblur has at some point implemented various anti-spam checks on incoming newsletters, which are now causing false positives and rejecting legit newsletters. I run my own mailserver, so incoming newsletters go there and are then bounced to newsblur. Forcing things to ipv4 and making sure SPF is set up mostly works to get my newsletters past spamhaus and improvmx, but I’m still getting failures on some.
Given the access key required in the newsletter address, I’m not sure any spam detection should really apply if the recipient is valid.
Sample rejection message on a legit newsletter:
SMTP error from remote mail server after end of data:
550 5.7.1 Message considered as SPAM (Score of 5.2/5 with BAYES_00,
DEAR_FRIEND, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DMARC_PASS,
HELO_DYNAMIC_IPADDR2, HTML_MESSAGE, MIME_QP_LONG_LINE, RDNS_DYNAMIC,
SPF_HELO_NONE, TVD_RCVD_IP, T_KAM_HTML_FONT_INVALID) - ImprovMX v2026.01.28
I’ll add that the most recent bounces were originally sent from Bandcamp, Kickstarter, and Substack. Most newsletters from them are going through, so it seems the actual content must be tripping the Bayes spam score too high.
Can you please take a look at this? I’m seeing lots of bounces on newsletters from substack, patreon, kickstarter, etc., so they’re not making it to my newsblur feed.
Sorry for the long wait on this. You have it right, the rejections are coming from ImprovMX, which receives mail for newsletters.newsblur.com, and their SpamAssassin scoring bounces anything at 5.0 or above before NewsBlur sees it. NewsBlur itself doesn’t filter newsletters at all, and I agree the secret token in the address should be enough. I’ve asked ImprovMX to turn off filtering for our domain since the mail only goes to NewsBlur and never to a mailbox. If they won’t, the next step is moving newsletter delivery off ImprovMX entirely. I’ll post here when I know which.
This started happening on other newsletters so I finally took a look: WIRED Newsletters blocked as spam