To ensure that email sending from your system works reliably, you need to allow the following IP addresses in your firewall (whitelisting).

All clouds

• 3.68.17.137

CloudId: 92 (FFM) Frankfurt

• 3.73.157.175
• 3.74.108.181
• 3.76.111.188
• 18.157.119.21
• 3.127.102.109
• 3.64.31.1
• 3.66.158.117
• 52.29.99.213
• 3.124.238.31
• 3.124.161.7
• 18.192.226.2
• 2a05:d014:11e4:2d03::/64
• 2a05:d014:11e4:2d04::/64
• 2a05:d014:11e4:2d05::/64
• 2a05:d014:1894:da03::/64
• 2a05:d014:1894:da04::/64
• 2a05:d014:1894:da05::/64
• 2a05:d014:1b1d:3003::/64
• 2a05:d014:1b1d:3004::/64
• 2a05:d014:1b1d:3005::/64
• 2a05:d014:37b:5a03::/64
• 2a05:d014:37b:5a04::/64
• 2a05:d014:37b:5a05::/64
• 2a05:d014:14ef:b803::/64
• 2a05:d014:14ef:b804::/64
• 2a05:d014:14ef:b805::/64
• 2a05:d014:18c9:5f03::/64
• 2a05:d014:18c9:5f04::/64
• 2a05:d014:18c9:5f05::/64
• 2a05:d014:1c1e:1d03::/64
• 2a05:d014:1c1e:1d04::/64
• 2a05:d014:1c1e:1d05::/64
• 2a05:d014:1a21:cb03::/64
• 2a05:d014:1a21:cb04::/64
• 2a05:d014:1a21:cb05::/64

CloudId: 94 (IE) Dublin

• 54.154.162.148
• 79.125.52.145
• 52.212.95.76
• 54.247.73.56
• 54.229.55.143
• 52.49.205.57
• 18.202.38.60
• 2a05:d018:c17:f303::/64
• 2a05:d018:c17:f304::/64
• 2a05:d018:c17:f305::/64
• 2a05:d018:203:c503::/64
• 2a05:d018:203:c504::/64
• 2a05:d018:203:c505::/64
• 2a05:d018:19b5:ce03::/64
• 2a05:d018:19b5:ce04::/64
• 2a05:d018:19b5:ce05::/64