The complaint is usually accurate and the diagnosis is usually wrong. Writing that sounds robotic is rarely a grammar problem. It's three specific habits, and all three are learnable in the other direction.
Habit one: textbook formality
Business English materials teach a formality that's roughly thirty years out of date in most workplaces.
Please find attached herewith · I am writing to inform you that · Do not hesitate to contact me should you require any further assistance.
All grammatically correct. All signalling that the writer learned English from a book rather than from people.
The current equivalents are shorter. I've attached · Quick update on · Let me know if you need anything else.
Habit two: translated structure
Every language has a preferred sentence architecture, and carrying yours into English produces sentences that are correct and somehow off.
Common versions: very long sentences with multiple subordinate clauses, where English would use three short ones. Front-loading all the context before the main point, where English puts the point first. Nominalising everything — the implementation of the solution was undertaken by the team instead of the team implemented it.
The fix for all three is the same and almost mechanical: shorter sentences, active voice, the main point first.
Habit three: AI polish
Newer and now the most common of the three.
Running your draft through an AI tool to make it sound more professional reliably produces text that sounds like every other piece of AI-polished text — the same rhythm, the same connectives, the same evenness. Readers have started noticing, and a growing number read it as a signal that nobody actually wrote the message.
Using it to check grammar is fine. Using it to improve the style will remove whatever was yours about the writing, which is the opposite of the goal.
What makes writing sound human
Varied sentence length. A long sentence followed by a short one. The rhythm is most of what we hear as voice, and uniform sentences are the single biggest tell.
Contractions. I'll · don't · we've. Their absence makes writing stiff faster than almost anything else, and they're appropriate in nearly all professional contexts short of a contract.
Ordinary words. Use rather than utilise. Help rather than facilitate. Buy rather than purchase. The plain word is almost always the better one, and reaching for the longer one is the most recognisable marker of someone trying to sound professional.
Saying something specific. The numbers came in lower than we expected and I think the forecast needs revisiting has a person behind it. Performance metrics indicate a variance requiring further analysis does not.
A practical test
Read it aloud. If you would not say it to the person in a conversation, don't send it to them in writing.
That single check catches most of it, and it's the one habit worth keeping permanently.