I connected a newsletter signup form on my website to it's email list using the API key from my mailing list provider (think Aweber, Mailchimp, etc).
Everything was working fine, until one day, the connection did not work anymore.
My hosting company said everything was fine on their end
My mailing list provder said everything was fine on their end
My wp newsletter signup plugin provider said everything was fine on their end.
After days of agony, it turns out that many mailing list providers use the company Akamai to automatically filter out bad ip adresses.
Since I was on shared hosting, hundreds of websites shared my IP.
1 of these other websites did something bad, and the IP was blacklisted by Akamai.
Possible ways around this were suggested:
1. Make your hosting change IP - they wouldn't, since it is shared hosting.
2. Upgrade to VPS said the hosting company
For now, I decided to use just the basic signup form from my mailing list provider, since no API is needed for that.
Just thought I'd let you know about this possible horror :-)
P.S. If you have other possible solutions, let me know!