### Clue: Mike has trouble with partner over online message (1-4)
### Answer: E-MAIL 
 ### Explanation: Definition: online message

**M** (Mike, in the NATO phonetic alphabet) *has* **AIL** ("trouble") *with* **E** (East, "partner" in bridge) *over*
 

 
*Not convinced by the E = East, but can't think of another explanation