If you are going to get heated about this at least read the bloody report...
"We further observe that Gmail marks a significantly higher percentage (67.6%) of emails from the right as spam compared to the emails from left (just 8.2%). Outlook is unfriendly to all campaign emails, more unfriendly to the left than to the right. It marks a higher percentage of left (95.8%) emails as spam than
those of right (75.4%). Yahoo marks 14.2% more left emails as spam than the right emails"
But have you considered the idea that the company generating GOP emails may be tripping spam filters due to the way they are written? The filters don't know where these came from but they will trigger on certain elements in the email - write less spammy emails and they will not be marked as spam
Also, it was found that if a person shows an interest in the political emails, Google's algorithm very quickly adapted so there was minimal bias:
"Moving All Spam Emails to Inbox. When a user moves emails from spam to inbox, the spam percentage should decrease because the user is showing interest that such emails should appear in the inbox. The response of Gmail to the S→I interaction follows this intuition while that of Outlook and Yahoo does not. The negative values for both the left and right emails for Gmail show that Gmail starts putting a higher percentage of emails from both sides in inbox after just the first S→I interaction. Fig. 7 shows that after the five S→I interactions, on average, Gmail marks just 5.34% of the right emails as spam (compared to 67.6% in the baseline experiment)"
Incidentally, when the same move of email from spam to inbox occurred in Outlook and Yahoo, the bias towards the Right actually increased slightly.
"To summarize, due to the S→I interaction, the political bias in Gmail reduced significantly. However, unexpectedly, it increased in both Outlook and Yahoo because neither of the two services reacted noticeably to user’s desire to not mark the emails as spam that the two services were marking as spam"
Republicans are cherry picking the results and shouting loudly about bias without admitting that
1) Some form of bias is probably just a by-product of generic spam filters and the way the emails are formatted
2) Outlook and Yahoo are biassed towards Republicans
3) With very minor tweaks, republican voters can all but remove any bias in the spam filters
I can't speak to Twitter and Facebook as I don't use either and have little interest but this is largely another GOP attempt to play the victim card with little evidence