Can't send E-mails from Gmail using E-mail clients on our network

Hi there,

So, I've got a weird problem with Gmail. For some reason, I can receive E-mails just fine using E-mail clients (namely, I've tried Evolution and Claws Mail), but I can't send E-mails (via SMTP) using this account. This only occurs on our local network (both WiFi and Ethernet); I'm able to send E-mails at my university's network with the same settings with Claws Mail.

This is what Google says about getting E-mail clients to work with Gmail (I added in dashes to maintain the indentation they use):

> If you're using a client that's not listed above, you can also use the
> following information to configure your IMAP. If you have problems, contact
> your mail client's customer support department for further instructions.
>
> ----Incoming Mail (IMAP) Server-Requires SSL
> --------imap.gmail.com
> --------Port: 993
> --------Requires SSL:Yes
> ----Outgoing Mail (SMTP) Server - Requires TLS
> --------smtp.gmail.com
> --------Port: 465 or 587
> --------Requires SSL: Yes
> --------Requires authentication: Yes
> --------Use same settings as incoming mail server
> ----Full Name or Display Name: [your name]
> ----Account Name or User Name: your full Gmail address (name at domain). Google Apps users, please enter name at domain
> ----Email address: your full Gmail address (name at domain) Google Apps users, please enter name at domain
> ----Password: your Gmail password
>
> If your client does not support SMTP authentication, you won't be able to
> send mail through your client using your Gmail address.
>
> Also, if you're having trouble sending mail but you've confirmed that
> encryption is active for SMTP in your mail client, try to configure your
> SMTP server on a different port: 465 or 587.

For both Evolution and Claws Mail, I have tried the default port (25) and both of the ports Google suggests. On Evolution, I've tried using SSL instead of TLS and Login authentication instead of PLAIN.

The odd thing is I also have a Lavabit account, and this one works just fine in both Evolution and Claws. It is set on Evolution to use port 587, TLS encryption, and PLAIN authentication, and on Claws it is set to use the default port (25), TLS encryption, and "Automatic" authentication (I suppose that means it figures out what to use automatically).

Has anyone else had similar problems with Gmail? Or is there maybe something I don't know about using E-mail clients that I'm neglecting?