Government officials may meet one on one with potential offerors provided no vendor receives preferential treatment. Moreover, even after the solicitation is issued, FAR Part 15 encourages exchanges of information with interested parties up until the time for receipt of proposals. There is no requirement that all possible offerors be involved and one on one meetings are permitted. The only warning is that any information shared in a meeting that could directly affect proposal preparation must be shared with all potential vendors. That's the law. And we have paraphrased from Dan Gordon's myth busting memorandum.
Restricting communications during debriefings (to say nothing of doing them by email) will not prevent a protest. Protests are rare and rarely successful. Contracting officers should concentrate on conducting meaningful and constructive communications during the course of the procurement. If they do so, issues that could cause protests can be eliminated. Again, this is straight from Dan Gordon's myth busting memorandum. Frankly, in our experience, failure to conduct a thorough, face to face, meaningful debriefing causes more protests. Hiding behind a few choice platitudes in an email often leads to protests just to find out the information which could have been divulged at the debriefing.
Finally, FAR 15.506(d) says "at a minimum, the debriefing information shall include" six, count them, 6, items of information. At a minimum. And look at that list: the complete evalutation of the offeror's proposal, the overall evaluated price and technical rating of the successful offeror and the debriefed offeror, the overall ranking of all offerors, a summary of the rationale for award and reasonable responses to relevant questions about whether the agency followed the evaluation criteria in the solicitation and the applicable regulations.
Always ask for a debriefing. Cite the regulation. FAR Part 15 applies in one shape or another to nearly every procurement. Dan Gordon's memorandum applies to all acquisitions and is based on a sound analysis of the regulations. In your request for the debriefing, cite FAR 15.506(d) and quote the list of items on the mandatory agenda.
It's time everyone paid attention to Dan's message on the government's duty to communicate.