If you're applying for a job, it's good practice to be more formal than typical. My wife is a teacher and even though the schools she works dress so that the children will feel comfortable, it's still well known that when applying for teaching jobs you wear a suit. (Although, one time her jacket was lost and she still got the job, but any online guide will tell you this is the exception.)
The same goes for correspondence, don't become less formal until the other person does. Even then, it's best not to become quite as informal as them.
I doubt anyone has lost a job due to writing 'kind regards' or 'thank you for your consideration'.
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Diagnosed with:
Moderate Hearing Loss in 2002.
Autism Spectrum Disorder in August 2015.
ADHD diagnosed in July 2016
Also "probable" dyspraxia/DCD and dyslexia.
Plus a smattering of mental health problems that have now been mostly resolved.