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Unable to receive e-mails through Outlook Gmail IMAP account- ports blocked by TMG 2010

Posted on 2011-09-19
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Last Modified: 2012-05-12
We are trying to enable external users to send & receive e-mails through their Gmail accounts.
I have setup a Gmail Imap account in Outlook and opened ports 995 & 465 on our TMG 2010 firewall (Internal > External- All users). This allows me to send e-mails through the Gmail account.
The error message I encounter in Outlook when attempting to receive e-mails is: "Task 'Synchronizing subscribed folders for marco@tcpnet.co.uk.' reported error (0x800CCC0E) : 'Outlook cannot synchronize subscribed folders for marco@tcpnet.co.uk. Error: Cannot connect to the server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP).'"
We do not use TMG client software.
Do I have to add another TMG access rule to allow incoming IMAP connections or am I missing something more fundamental here?
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Question by:mark-199
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by:Aaron Tomosky
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by:mark-199
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Port 587 is for the outgoing IMAP connection to Gmail and that already works fine; it's the incoming connection that is the issue.
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by:Aaron Tomosky
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The article says 993 for incoming, you have 995.
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by:mark-199
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Ok thanks but I've actually realised that this would have to be an incoming rule and I had it setup as an outgoing rule. What are the dangers of opening one TCP port to the entire network? I'm sure that this would be quite dangerous. Does anyone know how to setup Gmail Imap & SMTP mail flow specifically on TMG 2010?
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Aaron Tomosky earned 500 total points
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No, it's outgoing. You need 993 outgoing to receive mail.
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by:mark-199
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That's great it works. For my reference would you mind clarifying why both send and receive uses OUTGOING ports? Is it because I am requesting e-mails internally, which makes it an outgoing request? I guess if Gmail pushed e-mails to clients, I'd have to open inbound connections. Is that correct?
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by:Aaron Tomosky
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The connection is initiated on the LAN to the wan. That's outgoing. It doesn't matter that it's for receiving or sending mail. It's just a connection on a port TO gmail's servers.
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by:mark-199
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Thank you
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