Homeless people are being denied access to public services because they do not have a fixed postal address, according to a report.
Citizens Advice said the homeless could have their benefits sanctioned, drop down waiting lists or miss out on offers of housing.
The Royal Mail said it was open to the idea of providing Post Office Boxes for homeless people and was waiting for clarification on whether they would be a legitimate form of verification for services.
Citizens Advice called for action to allow an estimated 320,000 homeless people in Britain access to postal services.
It pressed for a free PO box-type system to be set up for homeless people, giving them an address to put on applications.
The Government should carry out a review of homeless people's access to post and how it can be improved, said Citizens Advice.
Chief executive Gillian Guy said: "With Christmas almost upon us, many people will be eagerly awaiting post and presents from loved ones.
"However, if you're homeless receiving your post can mean much more - it can be the difference between sleeping rough or receiving long-awaited accommodation.
"Our recommendations provide a simple solution to this unnecessary and damaging cycle.
"We'd like to see Royal Mail and Post Office trial our recommendations and work with them to end this Catch-22 and help homeless people get back on their feet."
A Royal Mail spokesman said: "We are very open to the idea of providing PO Boxes for homeless people. In fact, this is something we have looked at before and which we proactively discussed with Citizens Advice. We wish to play our part in helping to solve this issue.
"We want to work with a range of stakeholders to ensure this is an effective solution. The key point would be to establish whether a PO Box would be accepted as a legitimate form of authentication and verification by a range of organisations including banks and public bodies like the NHS and Department for Work and Pensions.
"As part of the work we carried out on this project, we have already asked Citizens Advice to confirm whether PO Boxes, or other possible solutions, would be accepted as a legitimate form of verification for such services.
"We are waiting for clarification from them on this important point as they have undertaken to liaise with a range of service providers and come back with an answer.
"Our view is that a concerted effort across a range of public and private bodies would be needed to address this issue."
Heather Wheeler, Minister for Housing and Homelessness, said: "Having somewhere to stay and a place to call home is vital in helping those who are homeless rebuild their lives, and we are determined to make this a reality.
"We are investing £1.2 billion to tackle all forms of homelessness and our Rough Sleeping Strategy, backed by £100 million, will provide the support needed to help people off the streets and into homes.
"We will continue to engage with Citizens Advice on this work and it is encouraging to see that the Post Office have committed to playing their role in supporting those without a fixed address."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Victoria Jones / PA Wire.