US startup RPost on Wednesday accused Switzerland's postal service of intentionally violating patented technology for proving email messages have been delivered.

The California-based firm is asking courts in the US and Zurich to put the brakes on Swiss Post's IncaMail, which it claims "mimics" a Registered Email service it sells in those and other countries.

Swiss Post spokeswoman Nathalie Salamin confirmed that patent complaints were filed against it in California in December and in Zurich in February.

Salamin denied the "IncaMail 3.0" service violated any patents and vowed Swiss Post would defend its technology platform.

Registered Email is crafted to provide legal proof that a message and its contents made it to a recipient, RPost co-founder and chief executive Zafar Khan told AFP.

"It is CYA for email," Khan said, referring to steps taken to cover one's backside by documenting exchanges. "Most disputes happen because there is a question of who said what to whom and when."

RPost boasted a customer list that included law firms, governments, manufacturers, and insurance companies.

The US government began using RPost services about eight years ago and Registered Email became available in Switzerland in 2004, according to Khan.

IncaMail is a service that lets an email message be traced like a registered letter while insuring it can only be read by the stipulated recipient, according to the Swiss Post website.

RPost first accused Swiss Post of patent infringement when IncaMail was introduced in the United States last year.

IncaMail was pulled out of the country after a confidential deal with RPost to settle the patent dispute. Swiss Post returned to the US in recent months with a revamped version of IncaMail.

RPost renewed their US case in federal court and sent the Swiss Post chief executive notice from Los Angeles using the IncaMail email service, according to Khan.

"They are using Swiss dollars to create a service that mimics what we already have in the market and ignoring property rights," Khan said.

RPost claimed to hold a combined 31 patents in 21 countries. The startup on Feb. 15 petitioned a commercial court in Zurich for an injunction to halt IncaMail there on grounds it infringes on two RPost patents in Europe.

"We have to take the fight to their home territory in Switzerland to put a stop to it," Khan said.

Swiss Post has until March 17 to file a response to the complaint with the court, according to RPost.

"We will now see if Swiss Post executives feel that they are above the law in Switzerland," Khan said.

"To put it simply, this is a matter of an agency of the Swiss Government using Swiss taxpayer dollars to knowingly and unlawfully use RPost's intellectual property. It is shocking behavior on the part of a government formerly renowned for its respect for the rights of individuals."

RPost made a similar petition in a California federal court based on US patents it argued are being violated by Swiss Post.