Earlier this month, news broke out that Bellsouth was suddenly and mysteriously blocking HTML email. We kinda blew it off, because ISPs try new tactics to block spam all the time, and sometimes things start off drastic, then they scale back a little (after enough customers complain). In email marketing, it’s always 2 steps forward, 1 step back.
Yesterday, while sending some HTML test emails to our Bellsouth test account, we noticed they weren’t showing up in our inbox at all (this is why it’s important to have accounts at different ISPs—if you can afford it). Then we remembered all the news about how Bellsouth was blocking HTML emails. Could it be they were actually serious about this?
Then we noticed that our Bellsouth account was receiving HTML emails just fine from Crate & Barrel (it helps to subscribe to other newsletters with all your test accounts, so you can see if you have problems, or if everyone else has problems too). Anyways, we analyzed Crate & Barrel’s email headers, and saw that they’ve implemented DKIM authentication.
Could that be it? We used one of our MailChimp customers’ accounts (who opted for our dedicated IP address add-on with full SenderID and DKIM authentication) to send an HTML email test to Bellsouth, and sure enough, it showed up just fine.
So it appears Bellsouth is blocking HTML email unless it is DKIM authenticated. They could be accepting SenderID as well, but our test had both forms of authentication on, so we’ll have to do further testing to see if they allow just one or the other.
What to do? Download your list and see if a very large proportion is using Bellsouth. If not, don’t worry too much. You can switch them to plain-text mode if you want (other people have been recommending that solution, so we assume Bellsouth is accepting plain-text emails that aren’t authenticated). If it’s "mission critical" for those recipients to get your HTML emails, you can implement DKIM. Note: you will need a dedicated IP address to implement DKIM. There are many other advantages to having your own dedicated IP (such as email certification). MailChimp users can get a dedicated IP with our "PRO" add-on. Details here.