The Ministry of Defence has launched an investigation into a data breach involving the details of 250 Afghan interpreters.
Email addresses could be seen by all recipients and showed people's names and some associated profile pictures.
It is not yet clear if the interpreters in question are in the UK or Afghanistan after dozens were left behind following the withdrawal of UK troops from the country last month.
It was sent by the team in charge of the UK's Afghan Relocations and Assistance Policy (Arap), which has been in contact with them since the Taliban took control of the country last month.
The team told the interpreters it was doing everything it could to help relocate them.
It also said they should not put themselves or their families at risk if it was not safe for them to leave their current location.
Former Defence Minister Johnny Mercer said the data error likely means Afghan translators would be "moving house again tonight".
He tweeted: "The truth on how we have treated our Afghan interpreters will come out.
"All the back slapping over Operation Pitting masks a criminally negligent performance by the Ministry of Defence and the Home Office on doing our duty to these people.
"I reiterate, the vast majority have been left behind, probably moving house again tonight."
This is the second major data breach from the MoD this year, after sensitive documents were discovered at a bus stop in Kent in June.
An MoD spokeswoman said an investigation had been launched into what Mr Wallace called an "unacceptable breach".
"We apologise to everyone impacted by this breach and are working hard to ensure it does not happen again," she said.
She added that the MoD "takes its information and data handling responsibilities very seriously".
Official Home Office figures show more than 8,500 former Afghan staff and their families, as well as Afghans who could be under threat from the Taliban, were evacuated to the UK during the August evacuation operation under the Afghan Relocations and Assistance Policy (ARAP).