Category: Spam/Antispam

Use DMARC to harden SPF and DKIM
article #1255, updated 50 days ago

The following TXT record:

v=DMARC1; p=reject; pct=100; adkim=s; aspf=s

at least theoretically, should harden SPF and, if present, DKIM. “=s” means “strict”. According to DMARC documentation, DMARC can be used without DKIM, and experiences with a first setup of the above without DKIM are playing out well so far.

Some info is here:



How to Check Spam Blacklists (RBLs)
article #241, updated 2165 days ago

Here is an excellent tool to check if your IP or domain is on a spam blacklist (a.k.a. RBL):

Type “” for domain checks.

Another is here, IP only:

Both check rather large collections of blacklists, as you watch.