Why did I get an e-mail with a nonsensical header?

I recently got an e-mail with the title

=?utf-8?B? 8J+QtiBZb3UncmUgYSBzdHJvbmcgY2FuZGlkYXRlIGZvciBvdXIgZnV0dXJlLCBQZXRlciDwn4e6 8J+HuA==?=

Thinking it might be malware, I ran a check with Malwarebytes, and it came up clean. Is there any legitimate reason for the title to be a nonsensical string of characters?

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