Every other letter from dear friends went astray (5)
I believe the answer is:
erred
'went astray' is the definition.
(I've seen this before)
'every other letter from dear' is the wordplay.
'every' becomes 'er' (I can't justify this - if you can you should give a lot more credence to this answer).
'other' indicates anagramming the letters.
'letter' becomes 'a'.
'from' indicates named letters should be taken away.
'dear' with 'a' taken out is 'der'.
'der' anagrammed gives 'red'.
'er'+'red'='ERRED'
'friends' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for erred that I've seen before include "Committed a sin" , "Went wrong" , "Made mistakes" , "Sinned" , "was inaccurate" .)