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Does Thunderbird able to work with IMAP-SMTP server via http-proxy (Squid) using CONNECT method? I saw proxy settings, but there is nothing about it.

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There is no mail passes through our squid proxy to Thunderbird. Proxy has turned-up CONNECT method for all SSLable ports. I think its because proxy settings in Thunderbird is for http-work only, but not for the IMAP and SMTP tunelling. Tell me pls if I wrong. If Thunderbird can work via proxy, usind CONNECT, how can I up this setting and check its work?

There is no mail passes through our squid proxy to Thunderbird. Proxy has turned-up CONNECT method for all SSLable ports. I think its because proxy settings in Thunderbird is for http-work only, but not for the IMAP and SMTP tunelling. Tell me pls if I wrong. If Thunderbird can work via proxy, usind CONNECT, how can I up this setting and check its work?

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Yea, you right, Google is. I saw this article (anyway thanks), but actually haven't understand, what is the exact reason of non-connecting of my Thunderbird to the IMAP/SMTP with switched-on proxy.

part of squid.conf:

acl SSL_ports port 25 143 443 465 587 993 8443 acl Safe_ports port 21 70 80 210 280 443 488 1025-65535 591 acl CONNECT method CONNECT http_access allow CONNECT SSL_ports <...>

Thunderbird settings: IMAP: mail.orgname.org, port: 143 SMTP: mail.orgname.org, port: 587 Proxy: dc1.localnet.local, port: 3128 use system proxy setting/manual settings - doesn't matter

In proxy there is negotiate_kerberos_auth, but all rules about "proxy_auth REQUIRED" are lower then http_access allow CONNECT SSL_ports

There is no any hard- or software like firewall, that may block ports.

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Part of the problem is that Squid is a HTML Proxy only. It may be possible to trick it into tunneling IMAP and SMTP, but that's beyond the scope of this forum. By any means, this is not a Thunderbird problem.

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Well, the question was exactly about the Thunderbird's ability to tunnel-working through HTTP-proxy. If "no", then "no". Will look for another solution.