Looking into this, it seems we should move over to only checking for status code in line with the old C++ implementation as well as any of the 5+ FOSS SMTP clients I checked. There is no precedent in either standards or other FOSS implementation for trying to match the string in the first place.
Bug 2068867 Comment 4 Edit History
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Looking into this, it seems we should move over to only checking for status code [in line with the old C++ implementation](https://searchfox.org/comm-esr78/source/mailnews/compose/src/nsSmtpProtocol.cpp#1441-1449) as well as any of the 5+ FOSS SMTP clients I checked. There is no precedent in either standards or other FOSS implementation for trying to match the string in the first place.