Responding to concerns that some of the Australian Defence Force's more than 2300 deployed troops could be disenfranchised by slow mail services to overseas theatres, the Defence Department said the Australian Forces Postal Office was reliable and serving members would be counted if they chose to take part in the non-compulsory survey.

The department has moved to give advice to personnel deployed on operations and exercises overseas about the survey, which will require the return of completed ballots by November 7.

Troops have been reminded to enrol with their deployed postal address through the Australian Electoral Commission, while the department has confirmed correct addresses for deployment locations in the Middle East, Africa and Asia.

A spokesman said Defence had released guidance reiterating the Australian Bureau of Statistics advice that participation in the vote was voluntary and limited to Australians on the electoral roll.

"This guidance also provides advice concerning the relevant dates for the survey and procedures for enrolment on the Commonwealth Electoral Roll," he said.

"Defence personnel are responsible for their correct enrolment and postal address; however, Defence is currently assisting those members who may be away during the period between the survey mailout and when the responses are to be returned.

"The AFPO system used by Defence personnel deployed on operations is a reliable and robust system that, with sufficient time, can meet the needs of those members wishing to participate in the survey," the spokesman said.

More information will be sent to troops once arrangements for remote participation and for people without access to mail are finalised by the Australian Bureau of Statistics, which is conducting the vote for the Turnbull government.

"Once confirmed, more information about these arrangements will be provided to Defence personnel deployed on operations and exercises," the spokesman said.

Defence will not allow campaigning for or against same-sex marriage ahead of the vote.

The largest groups of Defence personnel overseas include 780 people in the Middle East and Iraq as part of Operation Okra, a further 500 people in the Middle East for Operation Accordion and 500 people protecting Australia's maritime interests as part of Operation Resolute.

The ABS is working to provide arrangements for Australians in remote areas, travelling or working overseas and federal government personnel serving outside of Australia.

Some paperless voting will be provided for Australians overseas or who cannot receive ballots through Australia Post, with those eligible able to request a secure access code for voting.

Australians have until Thursday, August 24 to enrol or change their enrolment address.

Pending the outcome of challenges to the survey in the High Court, ballots will be mailed from September 12, with participants strongly encouraged to return their materials by October 27.

The results, broken down by "yes" and "no" votes and state, territory and national percentages will be released on November 15.