> None of it is backlinks provided to benefit some third party, and we've never participated in link swapping or anything like that.
The people sending out the e-mails don't necessarily know that though. Google won't tell sites which links are triggering penalties against them for obvious reasons, and there are a lot of spammy sites posing as user-generated content, far too many to manually review all the backlinks.
Worse, many of those sites aren't attempts at blackhat SEO for the pages they link but are actually trying to rank for particular terms themselves, but as far as I can tell Google doesn't make that distinction - if you're linked from a whole bunch of spammy sites you will now be penalized.
The people sending out the e-mails don't necessarily know that though. Google won't tell sites which links are triggering penalties against them for obvious reasons, and there are a lot of spammy sites posing as user-generated content, far too many to manually review all the backlinks.
Worse, many of those sites aren't attempts at blackhat SEO for the pages they link but are actually trying to rank for particular terms themselves, but as far as I can tell Google doesn't make that distinction - if you're linked from a whole bunch of spammy sites you will now be penalized.