BRUSSELS (Reuters) - German email service Tuta Mail has complained to European Union tech regulators about what it described as a sudden drop in Google search results on the day the bloc's new tech rules kicked in.

The European Commission last month launched investigations into Alphabet unit Google, Apple and Meta Platforms over potential breaches of the new Digital Markets Act (DMA), with Google's case partly focused on whether search results discriminate against third-party services.

Tuta Mail, which says it is the second-largest encrypted email service in the world with more than 10 million users, filed a complaint to the DMA taskforce on Tuesday.

"At the beginning of March 2024 Google suddenly stopped displaying our website for thousands of keywords, limiting search traffic to our site in large part to so-called 'branded traffic' only," the company said in its complaint seen by Reuters.

"This means people were no longer finding our encrypted email provider when searching for 'encrypted email', but only when explicitly searching for 'Tuta' or 'Tutanota'," it said.

Tuta Mail CEO Matthias Pfau said he does not understand why his company's ranking fell on the day the DMA became active.

"Obviously Google changed something in its search algorithms, but we do not know what they changed or why," he told Reuters in an interview.

"We have tried to get in contact with Google to discuss this issue, but have received radio silence."

Google said it does not unfairly promote its own products. Tech experts said websites can lose Google ranking due to algorithm changes.

"Search ranking updates absolutely do not aim to preference Google products, or any other particular website. The email provider in question is easily accessible globally on Search," a spokesperson said.

"We appreciate the feedback and will look into how we can ensure Search continues to return the most helpful, relevant results."

The Commission declined to provide details.

"The Commission monitors compliance of gatekeepers with obligations, including in the context of on-going proceedings. We cannot comment on specific concerns being raised with us," a spokesperson said.

Pfau said the impact on Tuta Mail has been dramatic.

"After removing most branded keywords, we see that our total impressions per month (30 days) dropped by 88.47%. Google took away about 90% of our visibility online," he said.

"We want the DMA taskforce to include our data in their investigation on whether Google is complying with the DMA," he said.

The DMA obliges Big Tech to give rivals and users more choice, such as by allowing competing services to function with theirs while a list of prohibitions means they can't treat their services more favourably in ranking than rivals.