iPhone users have been freaking out over emails they appear to have received from the past. When we say past, we mean the 1970s – before email was invented.

I just received an email on my phone that said it was from 1970 but was all greyed out and when I clicked it, it disappeared.

— Emma Wilson (@SonicOomph) March 4, 2016

According to recipients, who tweeted about the strange occurrence, the emails were “all greyed out” and when clicked on, “it disappeared.”

I just received an email on my phone that said it was from 1970 but was all greyed out and when I clicked it, it disappeared.

— Emma Wilson (@SonicOomph) March 4, 2016

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The message pops up when users are checking their email in different timezones.

Computers use UNIX time to make sense of times and dates and in this system January 1, 1970 represents 0, the Telegraph reports.

Despite this, iPhone users were still perturbed by the unusual date stamp in their inbox.

What the hell is this? An email from 01/01/1970. pic.twitter.com/7AltdDC7lj

— Cameron (@LFCameron7) February 27, 2016

Cool I got an email from 1970? What the? pic.twitter.com/kUT6xdrBtS

— Brittany Mowday (@BrittanyMowday) February 22, 2016

Email from 1970 mint pic.twitter.com/Jli1Kw9hpl

— georgia (@ge0rgiasc0tt) February 12, 2016

Wish I could read this email from 1970. Maybe I’m a time traveller? #iPhone pic.twitter.com/z1IgWChRNl

— Sophie Bridge (@sophiebridge) February 9, 2016

Just got an email from 1970. Pretty sure that’s not right. pic.twitter.com/y7HTiTNhtL

— David McCullagh (@mcculld) February 7, 2016

Just found an email from 1970…didn’t know emails existed then pic.twitter.com/w4pOmp59zN

— Shannon Carr (@ShannonCarr_10) February 5, 2016