A landlord recommendation letter is asked for by a tenant who is applying somewhere else. It is a short document and there is a right way to write it: state what you can show from the tenancy record, and stop. The temptation is to add a sentence about what the tenant was like, and that sentence is the only part of the letter capable of causing anybody a problem, including you.
The facts that belong in it
Your name and contact details, the property, the tenant's name, the dates of the tenancy and whether it is current or ended, the rent and frequency, and the payment record over the period. Whether the deposit was returned in full, if the tenancy has ended, is the other item a receiving landlord genuinely wants. Date it, sign it, keep a copy with the tenancy file.
Why to leave out the character sentence
A landlord's characterisation is an opinion that the recipient will treat as a fact and that the tenant may never see. Federal fair housing law reaches conduct that makes housing unavailable on protected grounds, and a subjective remark is where assumptions about a person surface. A factual letter is more useful to the recipient anyway, because facts can be weighed against their own criteria.
If the tenancy was difficult
Write what happened, not what you concluded. Arrears occurred in these months and were cleared on this date. The tenancy ended by agreement or by notice on this date. You are not obliged to volunteer a narrative, and you should not write something you would be uncomfortable defending. If you would rather not write at all, say so to the tenant rather than writing something lukewarm.
Confirm the tenant asked
Get the tenant's confirmation, in writing, that you may release the information and to whom. Requests arriving by email from an unfamiliar address are not evidence the tenant wanted it sent. This takes a minute, protects the tenant's information and protects you from having released it to somebody who should not have had it.
Questions people ask about landlord recommendation letter
Do I have to write one?
Generally no. Most landlords do because the tenant needs it and it costs minutes, but there is no obligation and a lukewarm letter helps nobody.
Can I say a tenant was difficult?
State what happened with dates rather than a characterisation. Facts are defensible and useful; opinions are neither.
Should I send it to the tenant or the new landlord?
To whoever the tenant has confirmed in writing, and copy the tenant. They are entitled to know what was said about them.