Posts sentimental thoughts on vacation (6)
I believe the answer is:
tweets
'posts' is the definition.
'sentimental thoughts on vacation' is the wordplay.
'sentimental' becomes 'twee' (I've seen this before).
'on vacation' suggests removing the centre (after the inside letters have vacated the word).
'thoughts' with its middle removed is 'ts'.
'twee'+'ts'='TWEETS'
(Other definitions for tweets that I've seen before include "Chirps social media postings" , "Posts made on Twitter" , "online comments" , "Social media messages" , "Sends social media comments, information, etc" .)