Added hint to skip ip check in acme-mailcow

docs/firststeps-ssl.md

@@ -9,6 +9,8 @@ By default, which means **0 domains** are added to mailcow, it will try to obtai
 
 For each domain you add, it will try to resolve autodiscover.ADDED_MAIL_DOMAIN and autoconfig.ADDED_MAIL_DOMAIN to your servers IPv4 address. If it succeeds, these names will be added as SANs to the certificate request.
 
+You can skip the IP verification by adding SKIP_IP_CHECK=y to mailcow.conf (no quotes). Be warned that a misconfiguration will get you ratelimited by Let's Encrypt! This is primarily useful for multi-IP setups where the IP check would return the incorrect source IP. Due to using dynamic IPs for acme-mailcow, source NAT is not consistent over restarts.
+
 You could add an A record for "autodiscover" but omit "autoconfig", the client will only validate "autodiscover" and skip "autoconfig" then.
 
 For every domain you remove, the certificate will be moved and a new certificate will be requested. It is not possible to keep domains in a certificate, when we are not able validate the challenge for those.