On 2023/10/06 10:09, Marco via mailop wrote: > Hello! > > I have an IPv6 and IPv4 accessible server, both protocols work and I > receive mails with IPv6 too. > Although, I see that certain IPv6 capable servers send with IPv4 in > some cases. > I am not aware of any outages and the strange things is it is rather > random which protocol they use. > > relay=mx.mailop.org [91.132.147.157] #never sent me mail via IPv6, but > I can send to them via IPv6 > relay=bendel.debian.org [82.195.75.100] > relay=bendel.debian.org [IPv6:2001:41b8:202:deb:216:36ff:fe40:4002] > > What can be the reason for that?
Postfix balances address families by default to avoid blockages if one isn't working: https://www.postfix.org/postconf.5.html#smtp_address_preference https://www.postfix.org/postconf.5.html#smtp_balance_inet_protocols Perhaps some other MTAs have similar too. Some admins disable delivery over v6 completely because some receiving sites are suspected to apply more stringent checks to mail coming in over v6. Some just do this for specific sites (e.g. as shown in https://www.postfix.org/postconf.5.html#smtp_dns_reply_filter), some for everything. _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
