Known Provider Limitations
Here is a list of limitations imposed by email providers that you should be mindful of during your acquisitions. These limitations are not specific to FEC but apply globally to all email clients.
Yahoo and AOL
We have received reports that Yahoo/AOL is capping folder listings over IMAP to 10,000 items per subfolder. This cap is applied before an in-place search is executed.
1. For Yahoo, using the server export.imap.mail.yahoo.com instead of imap.mail.yahoo.com, and for AOL, using the server export.imap.aol.com instead of imap.aol.com works around the 10,000 item limitation.
UPDATE: We have received reports that the export.* Yahoo and AOL servers intermittently cap folder listings at 100,000 items per subfolder. In some cases, the folder's item count is reported as being more than 100k items, but the list of items returned is capped at 100k. In other cases, the folder's item count is reported as 100k, but a complete list of items is returned.
UPDATE 2: FEC 3.85 and later can now bypass the 100,000 items per subfolder limit imposed by Yahoo and AOL.
2. We have received reports that connecting to Yahoo/AOL over POP3 bypasses the 10,000 item limitation. However, POP3 can only access the Inbox by design. So, this is not a complete workaround and could only be used to supplement your acquisition of the Inbox folder.
We have found that Yahoo/AOL is capping in-place search results via IMAP to 1,000 items per subfolder. In our testing, this does not apply to date-only searches targeting the Internal Date message attribute. It does, however, apply to participant searches.
Potential workaround—if you are hitting the search cap, we recommend acquiring the mailbox in full and performing your search post-acquisition.
When using the "search" query parameter, Graph API limits search results to 275 items per subfolder. To work around this limitation, FEC defaults to using the "filter" query parameter with Graph API. It is also possible to use EWS or IMAP on Microsoft accounts where applicable.
Some versions of on-premises Exchange 2013 Enterprise and Standard cap in-place search results at 250 items.
Potential workaround—according to Microsoft's support article, the issue can be resolved by installing an update and making a configuration change.