Perhaps if you were to offer the details of the provider we might be able to be specific.

Essentially you have been advised the server is detected as an exchange server. Very common these days with various cheap hosting packages particularly. It often also makes authentication very difficult without using an addon (OWL) using a native Microsoft protocol.

IF IMAP works fine, just be aware when you hear of exchange vulnerabilities on the news, you might be affected.

Thank you for your quick response, Matt.

I'm not sure what details you want about my provider. Per Wikipedia: "Sonic is a telecommunications company and internet service provider based in Santa Rosa, California, acting as a competitive local exchange carrier in the San Francisco Bay Area, Sacramento, and Los Angeles.[2][3] "

Many people here use it for its fast (fiber-optic) and reliable internet connections, its net neutrality and as an alternative to AT&T.

As I said, the customer service person I spoke with at Sonic said this message had nothing to do with them, but it sounds like you're saying that it has to, correct?

Could Thunderbird be detecting this local exchange carrier and incorrectly identifying it as associated with Microsoft?

Hello

don't worry about that, it's a misleading message.

Thunderbird has 3 ways of finding configuration information: - a static database more or less updated by volunteers: it's the last line before giving up if direct autoconfig do not work. - a method conforming to standard internet autoconfiguration: browse to example.com/.well-known/.... - a method conforming to Microsoft 'standards', defined for Microsoft servers: browse to autodiscover.example.com....

Sonic.net has apparently not bothered to use standard internet configuration, but implemented the Microsoft one. It's a Microsoft protocol, so Thunderbird is assuming it's a Microsoft server. However, Sonic don't use Microsoft servers, it's only implementing autodiscover mail settings like that because it's only caring for Microsoft *clients* (in other words, Outlook), or software clients that are able to also use Microsoft protocol (for example Thunderbird). In other words, if it works, don't waste your time fretting like that.

I received further clarification from Sonic. They stated: "Starting around November 1st, Microsoft's discovery service started providing incorrect information for Sonic.com. ... it [my question] could be related to this error" They further stated that "Microsoft is not in any way involved in sending or receiving of emails for Sonic" and recommended that I manually configure the IMAP and SMTP settings in Thunderbird instead of using autodiscovery.

For other Sonic users: the settings for manual configuration can be found on the Sonic website (search "Quick Reference Guide"). Sonic also told me that "Normal password" is the correct choice for Authentication Method: "The connection is already fully encrypted when the mail client sends the password to our servers, so there's no risk from choosing this option."