If you have multiple forums, do you have a separate Mandrill account for every forum?
Or do you have them in 1 account?
1 thing I notice is that you can only set up 1 bounce account. I don't think that's going to work.
I run multiple websites (including multiple forums) - the sites I own are all in one Mandrill account while the others that are owned by my clients or by other companies that I own are in separate accounts.
I use Mandrill subaccounts to separate the statistics and control of each different site in my main account - with the subaccounts set by way of Mandrill rules.
However, there are two reasons you want to be careful running multiple sites in the one account:
1. a sudden drop in reputation of one site might cause problems across your other sites in the same account.
However, if you use tags and subaccounts you can usually see exactly where the problem lies and address it before it becomes a big issue.
I recently had a problem where one of my blogs was using a plugin which sends new-comment notification emails to people who commented on one of the posts. I think a bug in the plugin meant that people could not effectively unsubscribe from the updates, so someone started marking all the emails being sent as spam. Rather than marking the entire account as having a low reputation, Mandrill simply marked the tag being used for that function on that site - it helped me track down exactly where the problem was occurring (I was able to search on recently sent emails for that tag) and none of the other systems seemed to be affected.
2. there is a limit to the number of tags you can have in one account.
While you may only use a couple of tags for each site, if you have multiple sites you may find yourself getting close to that limit. Also be aware that the official WordPress plugin for Mandrill actually associates a different tag with each different mail sending routine in WordPress - so you may end up using far more tags than you had intended.
3. as you mentioned - there can only be one bounce account set up for a Mandrill account. I haven't actually gone down the path of integrating bounced email processing from Mandrill into XenForo yet (mainly because I do have multiple forums in the one account).
Also, I'm not sure I want all emails from the entire domain being sent to XenForo for processing - I run multiple non-forum services associated with each forum (HelpDesk, blog, CRM etc) and there are typically multiple email addresses being used which might all have different bounce requirements.
I need to spend some time designing a bounce management plan for my systems which includes linking in to the automated XenForo bounce processor. I may look at building a custom Mandrill webhook which parses bounced emails and sends those related to the forum on to the XenForo bounce processor for handling (bypassing the inbound bounced email mailbox). Haven't looked at the guts of this system yet to work out the best way of doing this - but it's on my todo list soon.
Assuming you only use Mandrill for your forum emails - having separate forums in separate Mandrill accounts would allow you to use the XenForo bounce processing by having bounced emails forwarded to your bounce mailbox by Mandrill.
I should see if anyone has suggested having multiple bounce destinations in Mandrill (eg one per subaccount) - because that would nicely solve this issue for most people.
