Any time you use an external service (like Kit) to send internal messages on behalf of your domain, allowlisting is typically necessary for inbox placement.
When using Kit to send messages to your own domain, it might be necessary for your IT team to allowlist Kit's IPs. This is because your domain sees that it is receiving a message from itself, but the message is coming from an IP address that it doesn't recognize.
To be safe, your mailbox settings might place the message in your spam folder. Allowlisting tells your mailbox that you trust Kit to send messages on your behalf.
Kit's IPs
To allowlist Kit, you'll want to send our IPs over to your IT team and ask that they allowlist them. Here are Kit's sending IPs:
168.245.119.110
167.89.80.227
168.245.92.169
168.245.98.99
167.89.29.250
167.89.29.34
167.89.3.15
167.89.80.33
168.245.126.179
149.72.157.114
167.89.105.164
149.72.157.113
149.72.214.208
149.72.201.182
167.89.86.243
167.89.91.222
167.89.30.32
167.89.30.57
167.89.31.253
167.89.80.39
168.245.93.138
168.245.5.113
168.245.50.52
149.72.39.237
149.72.174.164
149.72.21.245
192.254.115.187
149.72.61.159
149.72.60.6
168.245.97.130
149.72.161.220