Hi @Nitol IT
If I understand your question correctly, is the symptom like:
If this is the case, to me this may be a by-design behavior.
There is also a thread discussing about this: Exchange 2016 CU11 owa address timeout
Unfortunately to my knowledge there is no method to avoid this.
If you have sent to the recipient before (or have added the recipient as a mail contact in Exchange), you can use the auto-complete feature as a workaround to mitigate this issue.
And if you would like to submit your feedback to Microsoft about this feature, please consider creating a post in the Exchange feedback forum.
Thanks for your understanding.
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