A Massachusetts man pleaded guilty Thursday to sending threatening letters – one of which included white powder – to the Dallas office of the popular dating service OkCupid in 2017.

Liam MacLeod, 47, was arrested in February for sending the letter between September and December 2017, the U.S. Attorney’s Office for the District of Massachusetts said in a news release.

MacLeod, of Beverly, Mass., had been angry that the service banned him for violating the company’s terms of service, according to federal documents cited by the Dallas Morning News.

One of the letters sent to OkCupid’s Dallas office contained a “suspicious white powder” and the message: “Greeting from Beverly … Ban me will ya … Welcome to the wonderful world of ANTHRAX … Expect a package within the next couple of days … It won’t be ticking but it should be interesting!”

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Eight more envelopes came postmarked from Boston, according to a criminal complaint. Some of those letters contained a blood-like substance and references to a suspended account, the Morning News reported. Dallas County health officials determined none of the envelopes contained hazardous materials.

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Investigators were able to identify MacLeod by matching details in the letters with his suspended account. He pleaded guilty Thursday to two counts of mailing threatening communications and two counts of conveying false information and hoaxes.

Fox News' Nicole Darrah contributed to this report.