"Per my last email" is three words that mean: I already told you this. You did not read it. I am now telling you again, and I am documenting the fact that I already told you.
It is the most efficient passive-aggressive phrase in workplace communication. It accomplishes in four words what would otherwise require a paragraph of careful diplomacy.
The translation
"Per my last email" = I already said this. Please read my emails.
"As previously mentioned" = This is the second time I have said this. I am beginning to wonder if you are reading my emails.
"As noted below" = The answer is in this email. You did not scroll down.
"Circling back on this" = You did not respond to my last email. I am following up in a way that implies I am not following up.
"Just wanted to make sure this didn't get lost" = I know it did not get lost. I know you saw it. I am giving you a graceful way to respond without admitting you ignored it.
Why it exists
"Per my last email" exists because workplace culture generally discourages direct expressions of frustration. You cannot write "I already told you this, please pay attention." You can write "per my last email," which means the same thing but is technically professional.
It is a workaround for a communication norm that values politeness over clarity. The result is a phrase that is technically polite and functionally pointed.
How to avoid receiving it
Read the email before responding. Specifically, read the whole email, including the part after the first paragraph. Most "per my last email" situations arise because the recipient responded to the subject line without reading the content.
If you receive a "per my last email," acknowledge it directly: "You're right, I missed that — thanks for the reminder." This is more effective than pretending the phrase was not pointed.
The honest version: "I already covered this in my previous email, but here it is again for convenience." This is clearer, less passive, and equally professional. It is also rarely used, because "per my last email" has become the accepted shorthand.