[Resolved] A solution has been put in place. Users are now able to connect via SMTP to mail clients without timeout errors and the system is operating as normal.
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We are currently investigating an issue affecting SMTP (outgoing email) connections through third party mail clients. Users might be experiencing time out errors when trying to send mail from Outlook, Thunderbird, or Mac Mail. Sending through Webmail is not impacted at this time. The connectivity issues are only affecting some, and for those affected they may be successful upon a later attempt to send if it fails at first.