The appointment came after Barclays completed a strategic review of its email marketing requirements.
Cheetahmail will allow it to deliver email campaigns at a larger scale and benefit from an advanced reporting and analysis system.
Alistair Greenbank, head of online marketing and content at Barclays, said: "The level of sophistication offered by CheetahMail will enhance the relevance and quality of our email activity. The ability to monitor the effectiveness of email communications is an important change for us."
Denis Sheehan, chief executive of CheetalMail UK, said: "Today's announcement shows precisely why CheetahMail has become the first choice for sophisticated email marketers. We look forward to working closely with Barclays to help it achieve a quantifiable return on investment from its online marketing spend."
In May, Barclays chose Experian's Marketswitch software to improve the profitability, timing and delivery of its direct marketing to customers.
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