Opened a ticket and got a reply from Sendgrid on the blocking...looks like it's my random bad luck to be in an IP pool w/some spam-happy losers who are using Sendgrid for evil intent...one way (maybe only way) around this seems to be to open up a second Sendgrid account and hope I end up in a shared IP pool with better behaved members.
Nov 6, 2020, 2:38 AM PST
Hello! Thank you for reaching out to SendGrid Support Team! My name is Rares and I'll be more than happy to assist you in this matter.
Thanks for reaching out to us and reporting this IP blocklisting. When sending email through an account that is under the Free or Essentials pricing package, your account will be utilizing a shared IP pool. Being grouped with others in a pool of shared IP's can offer several benefits, especially if you are only sending a moderate amount of email.
Although there are benefits to sending on shared IP's, there are also risks which can sometimes produce unintended negative consequences. If some of these users display poor sending habits or behavior, it can negatively affect others (you) within the group.
There are many different blocklists, and not all are created equal. Blocklistings are usually temporary, but due to the nature of how shared IP sending works, they do come and go. The impact to an email program can be extremely varied usually depending on what domains you're trying to send to. For example, blocklisted IPs could have little to no negative impact on delivery for senders focusing their traffic to larger inbox providers, while sending to smaller domains or inboxes could have a higher impact.
Please know that SendGrid is unable to move accounts to different shared IP pools, but our systems will programmatically move accounts to different pools based on reputation and internal logic.
SendGrid is also unable to move IPs in and out of pools because it gives the impression of Snowshoe Spamming; A strategy where spam is propagated over several domains and IP addresses to weaken reputation metrics and avoid filters, which can make things worse. We do however proactively monitor our shared IP pools and attempt to mitigate all blocklisted IP's as soon as possible.