I use a spam filtering appliance from SpamTitan. For the last two days, I've not been able to receive email from Google domains (gmail or hosted) over IPv6...I get errors like this
Oct 27 13:25:55 mailfilter postfix/smtpd[9455]: lost connection after STARTTLS from paulie.lemoyne.amplex.net[2001:4950:1:b::3]
Oct 27 13:26:14 mailfilter postfix/smtpd[6357]: lost connection after STARTTLS from sylvio.lemoyne.amplex.net[2001:4950:1:b::2]
Oct 27 13:28:47 mailfilter postfix/smtpd[8473]: lost connection after STARTTLS from mail-oi0-x236.google.com[2607:f8b0:4003:c06::236]
Oct 27 13:28:49 mailfilter postfix/smtpd[9453]: lost connection after STARTTLS from mail-lf0-x230.google.com[2a00:1450:4010:c07::230]
Oct 27 13:29:01 mailfilter postfix/smtpd[5191]: lost connection after STARTTLS from mail154.gate137.n.mlgn2ca.com[188.131.137.154]
Oct 27 13:29:05 mailfilter postfix/smtpd[9331]: lost connection after STARTTLS from mail-oi0-x233.google.com[2607:f8b0:4003:c06::233]
Oct 27 13:29:06 mailfilter postfix/smtpd[10207]: lost connection after STARTTLS from mail-wm0-x22c.google.com[2a00:1450:400c:c09::22c]
Oct 27 13:29:40 mailfilter postfix/smtpd[9455]: lost connection after STARTTLS from paulie.lemoyne.amplex.net[2001:4950:1:b::3]
Oct 27 13:29:47 mailfilter postfix/smtpd[5189]: lost connection after STARTTLS from mail-qk0-x22d.google.com[2607:f8b0:400d:c09::22d]
Oct 27 13:29:56 mailfilter postfix/smtpd[6357]: lost connection after STARTTLS from mail-yb0-x230.google.com[2607:f8b0:4002:c09::230]
Oct 27 13:30:43 mailfilter postfix/smtpd[6886]: lost connection after STARTTLS from mail-yw0-x22b.google.com[2607:f8b0:4002:c05::22b]
Oct 27 13:30:49 mailfilter postfix/smtpd[6640]: lost connection after STARTTLS from mail-oi0-x22b.google.com[2607:f8b0:4003:c06::22b]
Oct 27 13:31:11 mailfilter postfix/smtpd[6808]: lost connection after STARTTLS from sylvio.lemoyne.amplex.net[2001:4950:1:b::2]
Oct 27 13:31:25 mailfilter postfix/smtpd[9453]: lost connection after STARTTLS from mail-qk0-x229.google.com[2607:f8b0:400d:c09::229]
Oct 27 13:31:37 mailfilter postfix/smtpd[10204]: lost connection after STARTTLS from mail-qt0-x233.google.com[2607:f8b0:400d:c0d::233]
Oct 27 13:32:51 mailfilter postfix/smtpd[9331]: lost connection after STARTTLS from mail-qt0-x246.google.com[2607:f8b0:400d:c0d::246]
Oct 27 13:33:05 mailfilter postfix/smtpd[10207]: lost connection after STARTTLS from mail-vk0-x233.google.com[2607:f8b0:400c:c05::233]
Oct 27 13:33:07 mailfilter postfix/smtpd[6872]: lost connection after STARTTLS from mail-oi0-x232.google.com[2607:f8b0:4003:c06::232]
Oct 27 13:33:09 mailfilter postfix/smtpd[9160]: lost connection after STARTTLS from mail-wm0-x22a.google.com[2a00:1450:400c:c09::22a]
Oct 27 13:35:56 mailfilter postfix/smtpd[6357]: lost connection after STARTTLS from paulie.lemoyne.amplex.net[2001:4950:1:b::3]
Oct 27 13:36:06 mailfilter postfix/smtpd[9331]: lost connection after STARTTLS from mail-qk0-x230.google.com[2607:f8b0:400d:c09::230]
Oct 27 13:36:16 mailfilter postfix/smtpd[6886]: lost connection after STARTTLS from mail-vk0-x231.google.com[2607:f8b0:400c:c05::231]
Oct 27 13:36:20 mailfilter postfix/smtpd[9453]: lost connection after STARTTLS from mail-yw0-x247.google.com[2607:f8b0:4002:c05::247]
Oct 27 13:36:27 mailfilter postfix/smtpd[9455]: lost connection after STARTTLS from mail-qk0-x235.google.com[2607:f8b0:400d:c09::235]
Oct 27 13:36:35 mailfilter postfix/smtpd[6808]: lost connection after STARTTLS from mail-yw0-x235.google.com[2607:f8b0:4002:c05::235]
Oct 27 13:36:39 mailfilter postfix/smtpd[5189]: lost connection after STARTTLS from sylvio.lemoyne.amplex.net[2001:4950:1:b::2]
Oct 27 13:37:05 mailfilter postfix/smtpd[6640]: lost connection after STARTTLS from mail-lf0-x230.google.com[2a00:1450:4010:c07::230]
The only "fix" I've found is to disable IPv6 on the appliance and remove my AAAA records, but I don't want to do that long term.