Your content can come across, and SMF is officially supported.
XenForo's importers are a separate (free) add-on from the customer area, and the officially supported sources are: XenForo 2, vBulletin, IPS, phpBB, MyBB, Discourse, and
SMF 2.0. The reason you didn't see 2.1 is that the officially listed version is 2.0, not 2.1. Because SMF 2.0 and 2.1 store their data almost identically, the 2.0 importer handles a 2.1 database in practice (people have done exactly this migration) - but since 2.1 isn't officially validated, the one non-negotiable step is a
test migration first: it lets us run your 2.1 data through the importer and iron out any edge cases before your real forum is ever touched.
What comes across: your members (accounts, emails, join dates), boards -> XF forums, topics -> threads, posts, attachments, and avatars. One note from the docs: all the importers bring data into the core forum, so there's nothing that imports into the XF Media Gallery - plain SMF has no gallery anyway, so on your side the Gallery would just be a fresh start (worth a check only if you were running a gallery mod). The one area that reliably needs a little hand-cleanup afterward is private messages (XF and SMF structure them differently).
The important part - the part I'd handle so you have zero surprises:
- Test migration first - always, and doubly so here since you're on 2.1. We import into a throwaway copy and verify everything before the real run. Your live SMF forum is never touched, so your existing content is never at risk. (XF's own docs note the import should run with the source and destination on the same server for speed - I'd handle that setup.)
- Integrity check - I compare counts before and after (users, boards, topics, posts, attachments) to confirm nothing was dropped, rather than assume it.
- 301 redirects from your old SMF URLs to the new XenForo ones. This matters for you specifically - you're getting traffic from YouTube and search, and redirects keep those links and your Google rankings working instead of breaking.
- PM cleanup - so your members' conversations land correctly rather than half-imported.
So directly: it's very doable, it's a well-trodden path, SMF is officially supported (2.0 importer, which handles your 2.1 data in practice), and the risk to your content is low when it's done carefully with a test run and verification. Happy to help you through it if anything.
