Microsoft's eventual goal to eliminate use of any passwords at some future point (which they deem not always secure) and instead move to other means of authentication, multi-factor, certificate-based or otherwise, has apparently also affected emailing options. If you were using a Microsoft SMTP setting and have intermittently been getting errors like "Error sending email: Unable to send email message using smtp.office365.com in area 13: Failure sending mail." or other errors in the past, and now email has failed altogether you may have not "opted in" to use legacy options, which allow use of passwords to authenticate. Here are articles with information or explanations:
https://office365itpros.com/2021/08/19/exchange-online-to-introduce-legacy-smtp-endpoint-in-2022/
After making the changes to opt in, one will need to use the smtp-legacy.office365.com server setting instead, with the designated mailbox to be used set up for legacy and appropriate options.
Note that an IT "Block Legacy Authentication" conditional access policy enabled for POP/IMAP/SMTP on all mailboxes may also inadvertently override a per-mailbox SMTP Auth setting if you don't add that mailbox as an exclusion in that policy. e.g.
Log in to your Azure tenant and go to Azure Active Directory > Security > Conditional Access Policies to list all CAPs and their On/Off state. Select one of the policies to view its settings. Use Users and Groups to see who it applies to (probably all users). Click Exclude and add mailboxes to exclude them from that policy, such as a Block Legacy Authentication IT has set up there. If blocking pop/imap/smtp authentication for all mailboxes, one may need to exclude the mailboxes to allow SMTP auth, then in Office 365 admin portal > active users > select mailbox > mail > mail apps enable the SMTP Authentication setting for that mailbox. That setting is overridden by the CAP unless the mailbox is excluded from it.
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3D convenience options for emailing allow use of basic SMTP to Send outbound emails only (3D is not a full or general email client and does not Receive any incoming email) similar to printers or scanners that similarly may allow emailing OUT items or documents but do not accept inbound emails. One is certainly not forced to use the emailing options inside 3D to deliver anything, but may choose to simply print or save their documents to PDF (usually by using Save > PDF in previews or printing reports to "PDF Document") and then in turn attach those directly in your regular email client to deliver. Or one may simply opt to use an alternative email like gmail or others that will allow basic SMTP sending from 3D (perhaps set an alternative box directly to simply FW any replies to your main box). 3D will not be able to address or update any legacy component options until after the current development cycle is finished and released (still in progress) so using an alternative email may also be an easier or quicker fix for the above issue.
Note that if you wish to switch to gmail for outbound emailing in 3D, this topic may prove useful, since Google also requires additional security options: https://3dinspection.com/en/component/cjforum/topic/10049-general-forum/office-management/440-gmail-5-5-1-authentication-required?Itemid=159
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