The most common and most likely answer to this crossword clue is the 5 letter word SPAMS
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P
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More clues leading to the result SPAMS
Buddy explains!

The straight part
We know that "Unwelcome communications" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unwelcome communications = spams.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SPAMS mean?
SPAMS noun- (rarely countable) Unsolicited bulk electronic messages.
- Any undesired electronic content automatically generated for commercial purposes.
- A type of tinned meat made mainly from ham.
- To send spam (i.e. unsolicited electronic messages.)
- To send spam (i.e. unsolicited electronic messages) to a person or entity.
- (by extension) To use (a spell or ability) rapidly and repeatedly.
- To post the same text repeatedly with disruptive effect; to flood.