When are recent email addresses removed from the iOS Recents list in Mail?

My clients have noticed that, if they change an email address for one of their contacts, and then create a new message and try to enter that contact in the To field, the iPhone still shows the previous email address in the Recents list.  How long does the iPhone keep addresses in recents, do they ever get deleted automatically when they age?

The affected clients are on iOS 11.2.5; they are Office 365 users and are using the native Mail and Contacts apps on the iPhone. They use Outlook 2016 Mac to edit contacts.
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JohnBusiness Consultant (Owner)Commented:
Did they re-sync the contacts from Outlook to the iPhone?  You must do this for the contact to change on the phone.

I sync from Outlook to iPhone with iTunes and upon completion of the sync, contacts have been updated.
RobertAtFoxAuthor Commented:
Thanks John!

I should have been specific; they sync 'over the air', and we know that once they make the change, the contact changes on the phone .

As a further example - lets say they have a contact John Jones, email address jj@email.com. They change John's contact so the email now reads jj@outlook.com

On the phone, this change reflects in contacts correctly. But when they start a new message, and type 'john jones' the suggested email addresses show two entries, one for each email, old, and new.
JohnBusiness Consultant (Owner)Commented:
Look in the Contact list in iPhone.  Is the contact new, old, or do you have both?  If the syncing was correct, there should only be new.
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RobertAtFoxAuthor Commented:
The contact is new and updated; no duplications, and the old info is gone.
JohnBusiness Consultant (Owner)Commented:
Try removing cached email contacts with this Apple Article below

Eoin OSullivanConsultantCommented:

You asked WHEN they will be removed .. or IF they will ever be deleted.

While there is still a "feature" where you can click the (i) icon beside the list of autofill names and REMOVE it from Recent as far as I'm aware that is not what you wanted to know.

Firstly there is NO option on iOS to purge all autofill emails that don't exist on the Contacts.

As far as I understand .. the autofill comprises a combination of the names/emails from the Contacts PLUS all the emails extracted from those found in the mail folders .. which will be marked with an (i) icon if they're not linked to a contact addressbook record.

So to use the example you provided.  If the email address is removed from the Contact record but the email is still listed on multiple emails in the Inbox or other folders in the Mail client then it will continue to suggest it in the autofill panel until you either
1. Delete all the emails that use that old email (to or from or cc)  .. and it will still take time for this to update iOS Mail autofill
2. Manually use the REMOVE option in the autofill dropdown to force its removal

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RobertAtFoxAuthor Commented:
Thanks! That clears it up and explains it.
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