SendGrid is our email service provider and may use varied IP addresses to send from. From time to time, these same IPs end up on block lists (such as Spamhaus or SpamCop).
SendGrid is aware of their IPs that end up on some block lists, but this is a constantly moving target as most RBLs are updated frequently.
Rather that chasing moving IPs, we have implemented proper sender authentication methods so that you may use SPF, DKIM, & DMARC to verify the authenticity of our emails.
If your spam filters aren't able to check SPF, DKIM, or DMARC, please whitelist the following domains & senders: