Hi,
After a pretty long exchange with the domain host, it looks like their outgoing spam filter marks the mail as spam and doesn’t let it leave the server. Here is a part of the report of their antispam tool that they provided me with:
5.50 BAYES_50
0.10 FREEMAIL_FORGED_REPLYTO
0.00 HTML_IMAGE_RATIO_04
0.00 HTML_MESSAGE
0.00 SPF_HELO_NONE
-0.10 SPF_PASS
After a lot of testing, it seems that the number of cyrillic characters triggers the bayesian filters to flag the mail.
The newsletter are made of blogposts written in russian, and after approximately 130 russian letters, the e-mails get blocked. Basically it works if I only include the post titles and limit the newsletter to the ~3-4 last blog posts. It used to work fine with titles+excerpt for 5-7 blog posts, weekly, but clearly their filter changed recently.
Sadly the provider’s support is telling me that there is nothing they can do. They are a french hosting company and I suppose they don’t have a lot of russian clients, so it is not something they are interested in fixing. They are recommending that I use a third party like MailJet, but that’s yet another added monthly cost.
I don’t think there is anything the plugin could do to help bypass their filter, but just in case I thought I’d ask: do you think there might be anything that can be done ?