Funnelback will strip out punctuation by default (generally replacing with a space) as these characters are not indexed. Having a look at the query as processed in the response packet of the data model will give some clues as to the actual query that was run by the query processor.
I would try specifying a phrase match for your query - try
meta_email="email@example.com" and see if that give you the result you want.
It's possible to tell the indexer to index some other characters too but you need to be very careful when using this because a number of the punctuation characters have a special meaning in Funnelback's query language.