The government might decide potential trustees were not independent, he cautioned, if Trump aides talked to them "before consulting" with the ethics office.
In contrast to most proposals floated by the Trump transition team, Shraub added that the ethics office only considers a trust blind if its underlying assets have "been sold off."
In his public remarks, Trump has mostly focused on who would manage the Trump Organization. He has not suggested he would divest, or sell off its assets.
The emails were obtained through a Freedom of Information Request from MSNBC and The James Madison Project, and represented by the law office of Mark S. Zaid.
Richard Painter, former ethics lawyer for President George W. Bush, says the email exchanges suggest the ethics office is "trying to touch base so they can take these issues seriously," while the Trump transition team evinces less "desire to sit down and work through the issues."
Norm Eisen, a former ethics lawyer for President Obama, offered ethics advice to Trump aides before the election, and has criticized Trump's approach to business conflicts since his victory.
"My view is that Office of Government Ethics and Director Shaub have been strong and outspoken in advocating ethics to the new administration, and this confirms it," Eisen said.
The ethics office provided hundreds of pages of material, including correspondence with and about the Trump transition team.
Much of the material reflects routine transition preparation, including ethics guidance, trainings and tutorials on how to file financial disclosures required by federal law.
The correspondence shows Trump transition officials provided financial information and email responses to the ethics office, reflecting a cooperative approach on many issues, while ethics office staff also sought more detailed and frequent interaction.
After some lapses in responses, there are government emails asking Trump officials if they "are still with the transition team," and a reference to the struggle to "pin" down Trump lawyer Don McGahn for a call. In one email, a Trump official acknowledges the "difficulty in getting touch with counsel's office," an apparent reference to reaching McGahn, who Trump has since appointed as his White House counsel.
While the Freedom of Information Act (FOIA) request sought materials about Trump's potential divestment from his company, that topic rarely arose in the materials, which included some redacted email.
Bradley Moss, a federal employment lawyer who oversaw the FOIA request, said that absence was concerning.
"Conspicuously absent is any evidence of the preparations allegedly being undertaken by President-Elect Trump to resolve potential conflicts of interest through some manner of divestment," Moss said.
"If the President-Elect's lawyers and compliance officers are not coordinating with OGE, who, if anyone, within the government are they coordinating on these matters?" he asked.
It is also possible that other correspondence on conflicts between Trump officials and the ethics office exists, but was withheld as privileged under federal law.
Trump announced and rescheduled a press conference to unveil more detailed plans for his business, now slated for next week.
While the email correspondence mostly shows behind-the-scenes preparations for a new administration, the apparent frustration of the ethics office with Trump spilled into public view in late November.
That is when the normally staid office posted several dramatic tweets about Trump's business plans, citing its past advice for Trump to divest.
The tone was so unusual, some asked whether the office's account had been hacked — including a government relations staffer for Twitter, who contacted the office.
The newly released emails add more context, showing those tweets came after Director Walter Shaub's concerned and frustrated emails to Trump aides. As another batch of emails obtained by NPR showed, it was Shaub who personally ordered the tweet-storm, telling an aide, "post them all at once."