No it does not. Good for you to notice. To completely disable IPV6, you must have an
inet_protocols = ipv4
entry.
But i prefer
to force postfix to send IPV4 only and receive any or all INET Protocol.
Edit postfix main.cf
Input these entries:
smtp_address_preference = ipv4
smtp_balance_inet_protocols = no
inet_protocols = all
It does send IPV4 only.
It is not good idea to send IPV6 FIRST (IPV6 should be used as a failover) to IPV 6 capable servers. Google started to complain in February (all was good until then) once my IPV6 got listed a month ago with Spamhaus and Google still keeps me in their internal lists (now they downgraded the server message saying YOUR messages contain dangerous links WTF). I was to blame for the listing because I was playing via telnet IPV6 and issued a wrong command and SPAMHAUS thought I was an app inside Ubuntu trying to send out). If you are testing IPV6 sending test with YANDEX mail. They dont care as they are Russians.
I just bought a micro AMD (30GB 1GB RAM) on Netcup for 12 EUR per year. And I do recommend it although Nextcloud seems slow (Recommended VPS host? - #16 by vele) and I have another one on OCI cloud. Netcup.de gave me a /64 IPV6 and OCI a /128.
Both instances are dual stack.
As for changing your IP you can always ask but OCI has a tedious manual PTR record procedure via Support ticket.
No Linode, never used one. Linode looks to me like Digital Ocean.
Hope this helps.
Cheers