import re
text = "system:microsoft flow:to_server vho:file-was-closed heur250:unknown.file, file.png:word, 03:00, file:123, mailto:user, cid:image003.png"
pattern = r'\bmailto:[\w.-]+|\b\d+:[\w.-]+|[\w.-]+:\d+|[\w.-]+:[\w.-]*\.(?:jpg|png)(?![\w.-])|[\w.-]*\.(?:jpg|png):[\w.-]+|([\w.-]+:[\w.-]+)'
print( [x for x in re.findall(pattern, text) if x!=''] )
aW1wb3J0IHJlCnRleHQgPSAic3lzdGVtOm1pY3Jvc29mdCBmbG93OnRvX3NlcnZlciB2aG86ZmlsZS13YXMtY2xvc2VkIGhldXIyNTA6dW5rbm93bi5maWxlLCAgZmlsZS5wbmc6d29yZCwgMDM6MDAsICBmaWxlOjEyMywgbWFpbHRvOnVzZXIsIGNpZDppbWFnZTAwMy5wbmciCnBhdHRlcm4gPSByJ1xibWFpbHRvOltcdy4tXSt8XGJcZCs6W1x3Li1dK3xbXHcuLV0rOlxkK3xbXHcuLV0rOltcdy4tXSpcLig/OmpwZ3xwbmcpKD8hW1x3Li1dKXxbXHcuLV0qXC4oPzpqcGd8cG5nKTpbXHcuLV0rfChbXHcuLV0rOltcdy4tXSspJwpwcmludCggW3ggZm9yIHggaW4gcmUuZmluZGFsbChwYXR0ZXJuLCB0ZXh0KSBpZiB4IT0nJ10gKQ==