Strain with money trouble in post overseas (7)
I believe the answer is:
airmail
'post overseas' is the definition.
'airmail' can be an answer for 'post' (airmailing is a kind of posting). I'm unsure of the 'overseas' bit.
'strain with money trouble' is the wordplay.
'strain' becomes 'air' (synonyms).
'with' says to put letters next to each other.
'money' becomes 'm' (abbreviation in economics).
'trouble' becomes 'ail' (synonyms).
'air'+'m'+'ail'='AIRMAIL'
'in' is the link.
Can you help me to learn more?
(Other definitions for airmail that I've seen before include "post far away" , "Way of communicating" , "Flying service" , "Postal service" , "Letter delivery system" .)