Have a small mail server, pretty low-volume (max bursts are 40-50 messages to Gmail, global volume to it is around 100 messages per week), delivering to gmail o

Have a small mail server, pretty low-volume (max bursts are 40-50 messages to Gmail, global volume to it is around 100 messages per week), delivering to gmail over IPv6. (Note: DMARC, DomainKeys and SPF all implemented) Mails are delivered reliably and have zero problems with it. Had man more issues with Yahoo, Hotmail and Apple, all of which only accept mail over IPv4.