Hello! My name is Ben a fellow member here in the community, not a Microsoft employee. Hope you are doing well!
It looks like you are using the Outlook on the web. Can you try going to your Outlook settings? Specifically, go to the Subscriptions part to check if the email you unsubscribe to is still listed.
You can try going to this link directly:
https://outlook.live.com/mail/0/options/mail/br...
If you cannot find it, try going to Settings > Mail > Subscriptions and find there the lists of emails you unsubscribed so you can subscribe back.
In case you need to have this specific service to resend the email to you, you need to reach out to them and request to resend this email so you can receive it again if they confirmed that you are already subscribed with them.
A similar post was also asked before on this community thread for reference:
https://answers.microsoft.com/en-us/outlook_com...
I hope the information how to proceed helos. Don't hesitate to post back in the community if you have other questions.