Link jam, surprisingly, with starter of unappealing spam (4,4)
I believe the answer is:
junk mail
'spam' is the definition.
'link jam surprisingly with starter of unappealing' is the wordplay.
'surprisingly with' is an anagram indicator.
'starter of' indicates taking the first letters.
The initial letter of 'unappealing' is 'u'.
'link'+'jam'='linkjam'
'linkjam' anagrammed with 'u' makes 'JUNK MAIL'.
(Other definitions for junk mail that I've seen before include "post to ditch" , "Reject post" , "Unwanted post" , "Unsolicited stuff" , "Depict in painting or words; highlight" .)