Is it permissible for a woman to travel alone to her husband who resides in another country, given that she does not have a mahram with her, and based on his request?

A woman is not permitted to travel except in the company of her husband or a mahram. However, if a mahram is unavailable and there is an urgent necessity or a dire need for her to travel, then there is no sin upon her for traveling without a mahram, provided she adheres to Islamic guidelines, such as observing hijab and being cautious about mixing with men, in addition to taking all necessary precautions.