The website, which incorporates content from the Daily Mail and the Mail on Sunday newspapers, attracted 29,872,465 users last month, up 1.7%, including 8,748,334 from the UK.
It marks the best ever performance by any UK newspaper website, pipping the previous record set by Guardian.co.uk with 29,811,671 uniques in January 2009.
Elsewhere, the summer holiday season appeared to take its toll on other websites across the sector.
Second-placed Guardian.co.uk saw unique users fall by 9.2% to 27 million, of which 9.9 million were based in the UK.
It remains just ahead of the Telegraph's site, which fell 7.8% to 26.5 million. Its UK users fell from 9.19 million to 8.7 million.
The site for News International's most popular daily newspaper, The Sun, proved more resilient despite the holiday exodus and maintained fourth place, with 25 million users. It was also the only major national newspaper to increase its UK users, from 8.7 million to 9 million.
In contrast, NI's quality offering Times Online was the biggest loser in July, falling 13.8% to 21,216,797.
The only other UK national newspaper site to increase its unique users last month was Mirror Group Digital, which incorporates content from , and .
Its unique users rose by 5.5% to hit 10.4 million with almost half, 5 million, located in the UK.
Meanwhile, IN&M's Independent.co.uk continues to haemorrhage users, dropping 12.5% to 8.4 million unique users, its lowest figure since last September. Its UK users also fell from 3.8 million to 3.7 million.
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