Microsoft have annouced they will be restricting access to Microsoft Teams data via EWS from the 30th September see https://devblogs.microsoft.com/microsoft365dev/restricted-access-to-microsoft-teams-data-via-ews-starts-september-30-2022/ . If you are using EWS to access any teams data you will need to move to the Graph API's https://docs.microsoft.com/en-us/microsoftteams/export-teams-content one thing to note is "Microsoft Teams APIs in Microsoft Graph that access sensitive data are considered protected APIs" so there are some extra steps and time you need to access this data and be aware of the potential need to pay for that access eg "On July 5th 2022, metered consumption is active, and will be billed through an Azure subscription" ref https://practical365.com/teams-export-graph-apis/.
Most email services these day employ Opportunistic TLS when trying to send Messages which means that wherever possible the Messages will be encrypted rather then the plain text legacy of SMTP. This method was defined in RFC 3207 "SMTP Service Extension for Secure SMTP over Transport Layer Security" and there's a quite a good explanation of Opportunistic TLS on Wikipedia https://en.wikipedia.org/wiki/Opportunistic_TLS . This is used for both Server to Server (eg MTA to MTA) and Client to server (Eg a Message client like Outlook which acts as a MSA) the later being generally Authenticated. Basically it allows you to have a normal plain text SMTP conversation that is then upgraded to TLS using the STARTTLS verb. Not all servers will support this verb so if its not supported then a message is just sent as Plain text. TLS relies on PKI certificates and the administrative issue s that come around certificate management like expired certificates which is why I wrote th