Workaround for Office 365 SharePoint Site Mailbox App mailbox name rewrite issue
My WorkaroundIn my scenario, the Client already had an internal established notation to prefix projects with the letter “p”. Therefore it would acceptable to prefix the project number with a letter.
1. For each existing or new SharePoint site you intend to add a new Site Mailbox App, temporarily alter the site name (Site Settings > Title & Description) to begin with a single letter. In this case, we altered all their existing Project sites in the format (note the “p” prefixed on the site title):
Site Title: “p193 My Project Name”
2. Deploy the Site Mailbox App. The email address generated will come out as in the style SMO-p193MyProjectName@site.onmicrosoft.com.3. Once Site Mailbox App is fully deployed, change the Title of the site in Site Settings back to “197 My Project Name” (without the “p”), therefore avoiding inconsistencies elsewhere including in document tags, metadata & last but not least, leaving people wondering why there’s a wacky letter at the start of your site title. J 4. That’s it, you’ve somewhat hacked your way around this strange little behaviour of how email addresses are generated when creating a Site Mailbox. Conclusion As for why the SharePoint Online system really does not seem to like email addresses that start with numbers, I have no info at this time. Certainly an address of SMO-193MyProjectName@site.sharepoint.com would meet general email RFC specs. Why the address comes out as SMO + alphabet soup + @site.sharepoint.com is a mystery and seemingly undocumented. I suspect it would be part of a secret sauce that only a select few MS Engineers may know – or it’s a simple pattern that’s obvious from the output email addresses. If anyone knows the reasoning behind the email address rewriting in play with site mailboxe, please do share in the comments!