The following regular expression will match each string and extract the postal code as group 1:
([\d\-]+)\s+[\w@\.]+
Here's the Python code to extract all of the postal codes at once:
import re
text = r''' 20530 mark@ucvxcx.gov
20530 kidafd@gmail.com
20530 vladfeodsaf@usdodfaadj.govv
20530 syadfadsbil.vvbvx@vnvnvn.gov
20004 safdbnvis9dfg@infdda.gov
20530 vhlhsdlf8dlfha@vbvbcxbUI.GOV
90012-3308 h.james@asdfad.gov
90012-3308 madsfl.hjlkdjd@pkdoi.gov
90012 mark.fraser@ruskgb.zx'''
re.compile(r'([\d\-]+)\s+[\w@\.]+').findall(text)