Aspin joined the firm in the early '90s, and most recently he has been leading a drive to raise the profile of direct mail as a marketing medium through the promotion of media-neutral planning.
Royal Mail would not confirm the news, and said Aspin was still at the company. A spokesman said that the company would not comment on individual relationships with employees.
However, a source close to Aspin has confirmed that he is to leave the company and has negotiated the terms of his exit.
Aspin's departure will fuel speculation about unrest at the company following a restructure of its marketing department, which saw only two members of the senior media markets team – Tim Rivett and Richard Roche – secure new roles.
The team was headed up by Adam Novak, who has moved to another division in Royal Mail, while David Higham and Derek Fairhurst left.
Last month it emerged that Higham had resurfaced at a Royal Mail rival, Dutch postal firm TPG Post.
Royal Mail restructured its marketing department in January, combining its sales and marketing departments to form a department of 300.
Royal Mail's business-to-business divisions -- media markets, business and consumer markets, and service delivery were replaced with one centralised department under managing director Jerry Cope.
The restructure saw the firm axe 100 jobs as part of chairman Allan Leighton's mission to streamline the business. The Royal Mail faces increased competition from competitors such as TPG and German postal firm Deutsche Post.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .