The following addresses are only for outbound SMTP customers. They are not required for spam filtering clients.  


This list was updated and shortened on Jan 1, 2020 with the netblock 204.27.244.0/24


Netblocks


104.232.45.0/24

204.27.244.0/24


Outbound SMTP


54.68.34.165
54.68.138.64
54.244.192.240
54.213.22.21
54.200.247.200
54.200.129.228
54.190.72.79
54.187.71.48
54.187.218.212
54.187.213.119
54.186.57.195
54.186.218.12
54.186.10.118
54.185.97.28
54.184.38.33
54.149.35.133
54.149.240.58
54.149.210.130
54.149.155.156
54.148.38.162
54.148.219.64
54.148.165.188
54.148.113.140


52.58.97.209
52.58.96.151
52.58.19.153
52.58.109.202
52.29.21.168
52.29.156.81
52.28.6.212
52.28.59.28
52.28.251.132
52.28.246.64
52.28.168.19
52.28.147.211
52.26.49.97
52.25.88.167
52.10.99.51
52.10.130.167


44.233.99.129
44.233.67.66
44.233.38.249
44.233.143.45


35.160.111.225
35.157.29.171
35.156.234.212


3.127.8.113
3.125.66.160
3.125.148.246
3.124.88.253
3.121.156.226


18.156.94.234
18.156.67.42


100.20.105.3


The attached file - duocircle_outbound_smtp_ip.txt has the full list of IP's that you can use to import into your firewall. Format text, one IP per line in CIDR notation.