By Tom Sims and Alexander Hübner

FRANKFURT, Nov 12 (Reuters) - Germany's financial regulator on Thursday fined Deutsche Bank €8 million ($8.9 million) over failures in the migration of customers from its Postbank unit to a shared IT platform.

The penalty from regulator BaFin draws a line under an embarrassing incident for Germany's largest lender.

In 2023, Deutsche Bank's integration of Postbank left customers locked out of their accounts and unable to reach call centres, triggering a wave of complaints.

The issue drew a sharp rebuke from BaFin and a public admission of mistakes from CEO Christian Sewing, dealing a blow to Deutsche Bank's efforts to rebuild its reputation after years of penalties tied to anti-money laundering controls and other compliance failings.

BaFin said Deutsche Bank "failed to put in place appropriate organisational arrangements to deal promptly with the increased volume of customer complaints arising from the migration of customer data".

"Furthermore, the company failed to execute orders for the transfer of securities accounts without delay."

Deutsche Bank said it had resolved the issues and had "continuously improved our processes since then".

"Deutsche Bank accepts BaFin's decision," it added.

BaFin was unusually outspoken in its criticism of Deutsche Bank. Its president described the problems as "unacceptable", it appointed a monitor at the bank and published data showing a surge in customer complaints.

The outages prompted a regional consumer group to call for legislation modelled on airline compensation rules that would require banks to compensate customers for service disruptions.

"A fine does not help customers whose accounts were blocked for weeks. We need a mechanism that compensates those affected, rather than merely punishing the violation," said Sascha Straub, who oversees financial services at the Bavarian consumer protection agency.

Sewing said at the time that Deutsche Bank had made mistakes in the Postbank integration and assigned hundreds of additional staff to address the problems.

Deutsche Bank began acquiring Postbank in 2008 during the global financial crisis, but struggled for years to complete the integration of the lender, which has millions of customers and roots in Germany's postal system.

Several members of Deutsche Bank's management board, including Sewing, took small bonus cuts as a result of the disruption.

($1 = €0.9027)

(Reporting by Tom Sims. Editing by John Mair and Mark Potter)

Find it fast

Looking for more insights? Explore our other news sections for updates on sustainable finance, companies and financial education