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The following ip6tables block thunderbird from retrieving email from my gmail account:

sudo ip6tables -P FORWARD DROP sudo ip6tables -P INPUT DROP sudo ip6tables -P OUTPUT DROP sudo ip6tables -A INPUT -j ACCEPT -i lo sudo ip6tables -A OUTPUT -j ACCEPT -o lo sudo ip6tables -A INPUT -j ACCEPT -m conntrack --ctstate ESTABLISHED,RELATED sudo ip6tables -A OUTPUT -j ACCEPT -m conntrack --ctstate ESTABLISHED,RELATED sudo ip6tables -A INPUT -p icmpv6 -j ACCEPT sudo ip6tables -A OUTPUT -p icmpv6 -j ACCEPT sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 53 -m comment --comment "DNS/TCP" sudo ip6tables -A OUTPUT -j ACCEPT -p udp --dport 53 -m comment --comment "DNS/UDP" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 22 -m comment --comment "SSH secure shell" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 80 -m comment --comment "HTTP" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 443 -m comment --comment "HTTPS" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 110 -m comment --comment "POP3" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 143 -m comment --comment "IMAP" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 993 -m comment --comment "IMAP/SSL" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 25 -m comment --comment "SMTP" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 26 -m comment --comment "SMTP 2nd" sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 465 -m comment --comment "SMTP/SSL"

Whenever I disable them, thunderbird can retrieve email fine. What am I doing wrong?

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  • At which stage is Thunderbird failing when trying to retrieve email? Commented Apr 25, 2020 at 6:54
  • Have you tried using the LOG feature of iptables to log which packets are being dropped? (you might be able to filter specifically thunderbird's packet if you run it as a different user and filter on that) Commented Apr 25, 2020 at 6:56
  • I repeatedly get this message: Apr 25 10:53:30 user kernel: message_out_ipv6:IN= OUT=enp0s31f6 SRC=fe80:0000:0000:0000:5fe0:8278:e978:29a1 DST=ff02:0000:0000:0000:0000:0000:0000:0002 LEN=48 TC=0 HOPLIMIT=255 FLOWLBL=587658 PROTO=ICMPv6 TYPE=133 CODE=0 I can't figure out what it means.. Commented Apr 25, 2020 at 9:55
  • May be this one? Apr 25 10:56:33 user kernel: message_in_ipv6:IN=enp0s31f6 OUT= MAC=33:33:00:00:00:01:c4:71:fe:8c:67:7f:86:dd SRC=fe80:0000:0000:0000:c671:feff:fe8c:677f DST=ff02:0000:0000:0000:0000:0000:0000:0001 LEN=72 TC=224 HOPLIMIT=2> Commented Apr 25, 2020 at 9:57
  • Please show the complete firewall, with ip6tables -nvL. Commented Jul 31, 2020 at 21:49

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What you see on logs or tcpdump? From other side some of Thunderbird and gmail tutorials (like https://oit.colorado.edu/tutorial/gmail-configure-thunderbird) suggest that it communicate with vendor site also on: Server hostname: smtp.gmail.com Port: 587 SSL: STARTTLS Authentication: Normal Password

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  • sudo ip6tables -A OUTPUT -j ACCEPT -p tcp --dport 587 did not solve it.. Commented Apr 25, 2020 at 6:35
  • Still - please check what you see in logs or TCPdump as first method. Commented Apr 25, 2020 at 7:38
  • I'm getting this message Apr 25 10:53:30 user kernel: message_out_ipv6:IN= OUT=enp0s31f6 SRC=fe80:0000:0000:0000:5fe0:8278:e978:29a1 DST=ff02:0000:0000:0000:0000:0000:0000:0002 LEN=48 TC=0 HOPLIMIT=255 FLOWLBL=587658 PROTO=ICMPv6 TYPE=133 CODE=0 Commented Apr 25, 2020 at 9:56