It looks like there might be a bug in our implementation of `nsIMsgOutgoingServerService::deleteServer` (defined [here](https://searchfox.org/comm-central/rev/56e10803273dbfdb9f28c5ba50c6d2e891debd42/mailnews/compose/src/OutgoingServerService.sys.mjs#106-118)) - it should definitely have at least removed the `ewsX` keys from `mail.smtpservers`. I don't think the underlying bug is specific to EWS, but I'll add it to the EWS bugs pile so we can investigate how trying to access bogus outgoing servers might impact account deletion (since EWS might be a bit strict when being used with an invalid config).
Bug 1936274 Comment 2 Edit History
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It looks like there might be a bug in our implementation of `nsIMsgOutgoingServerService::deleteServer` (defined [here](https://searchfox.org/comm-central/rev/56e10803273dbfdb9f28c5ba50c6d2e891debd42/mailnews/compose/src/OutgoingServerService.sys.mjs#106-118)) or whatever called it when you deleted your EWS account - it should definitely have at least removed the `ewsX` keys from `mail.smtpservers`. I don't think the underlying bug is specific to EWS, but I'll add it to the EWS bugs pile so we can investigate how trying to access bogus outgoing servers might impact account deletion (since EWS might be a bit strict when being used with an invalid config).