How to transfer mailboxes from V4 (Sierra) to V3 (El Capitan)

Locate the correct alphanumeric folder with your local "On My Mac" folders. Put this folder on your Desktop.

You have two options:

1) In Mail under File > Import Mailboxes... select the folder on your Desktop

(note sometimes this imports correctly but occasionally, it will bring it over as they show by size in Library)

2) Use Emailchemy to convert. Select Kind: Apple Mail. It will balk that it's not in the correct location, but it should export. I suggest you select to save as .MBOX File ("standard mbox") In Mail > File > Import Mailboxes > select "Files in mbox format.

3) Identify in the Mail (Sierra would be V4) folder that contains your local folders. (look for outbox). With Mail quit....Put the files inside the alphanumeric folder you dragged over into the current local alphanumeric folder. Next, in MailData, delete the 3 files with Envelope in the name. Open Mail, it will reindex your messages.

If y'all don't mind, I'd like to ask something that it similar in nature to the original thrust of this thread:

As time has since marched on, I have just upgraded--cleanly--to High Sierra from Sierra. To complement my TimeMachine backup I also did a manual backup of the entire system drive. My previous Mail had a nicely arranged archiving system that I'd like to continue in HS but now that it's just sitting on a random hard drive I cannot access the User Library. It remains invisible just as it is on one's system uses the Option key is pressed. No amount of searching reveals it.

I tried doing a TM restore back to the last saved Mail folder before upgrading but the button remained grayed out, leading me to wonder if V4 designation is incompatible with HS?

Will Emailchemy works with this dilemma? I did have subfolders aplenty in my archive, e.g. "Inbox" containing sub-boxes "2016," "2015," etc. Would this indexing transfer?

It did occur to me since my entire old system drive was copied over to this external drive I could restart out of that Sierra system and be able to access the old Mail that way, however the V4 compatibility question remains.

Any help appreciated

Right. No I was wondering if I could use it with the manual backup I had done on the separate drive.

All this may be moot because I may be going back to Sierra because my iMac is constantly crashing since upgrading to HS. Yay!

I repled to you on the other thread Mail move over to High Sierra" on how to get your folders back.

Emailchemy cannot work on data in Time Machine.

I hope this is appropriate to post my question:I recently tried to upgrade my MacBook pro to Sierra and got stuck in the process at a frozen apple icon. i could however tap into the hard drive and copy my mail folder as well as my preference file "com.apple.mail.plist.lockfile". Now I am trying to reinstall this in my new MacBook Pro with Sierra installed. My question. Do I just change the file name v2 for v4 and copy the old data into that dir.? And also do I place the plistfile into preferences? I hope this makes sense.thank you for u for your help

Have you used Mail on the new MBP?

If no, do these steps:

Place the V2 folder in Mail.

Open Mail and it will do the upgrade process of moving your data correctly into the V4 folder.

V2 should now only contain MailData folder. You can delete the V2 folder.

If yes, you only need to import the local "On My Mac" folders in MailBoxes folder.

Place the V2 folder on your Desktop.

In Mail, under File in the Menu bar select Import Mailboxes…

Select Apple Mail

Navigate to the V2 folder on your Desktop

Inside V2 look for the Mailboxes folder.

Import.

If you had POP account, you would need to import the other folders. No need to import the folders for IMAP account.

Let me know if there are any questions.

I did this once from an older OS version to the latest and it worked; it should work the other way around as well. Caution: it is extremely time consuming. Since the file structure is completely different, you cannot copy folders - you have to actually drill down and copy individual emails. Create the same folders on the receiving computer and then copy individual emails and put them in the receiving folder. Open Mail and before trying to open an email, rebuild all of the mailboxes - then try to open one.

Have you considered archiving or exporting them to your desktop, putting them in appropriately named folders, and then storing them on an external drive? You could free the Mail app of all of them except the current year and it'd be a lot easier.

It worked before because both computers were running the same version and therefore the files/folders were compatible. As you yourself pointed out they are different now - this is why Apple use a different version number.

It is extremely unlikely merely changing the version number in the folder name and copying them would work otherwise there would be no reason for Apple to have used a different version number. If you do remove the magic files leaving just the emails then Mail is likely not going to recognise them as valid.

An option you have already I believe discounted is to in Sierra export as MBOX files, these can then be imported on the El Capitan machine. While this is far less work than doing each email individually with the quantity of folders and messages you describe it is still going to be a lot of work but at least this is an officially recommend solution by Apple.

Something else to consider would be upgrading the El Capitan Mac to Sierra then once again both will be using the same version and hence be compatible. However I am guessing maybe your El Capitan Mac is not Sierra compatible.

Since you say the desktop was upgraded to Sierra it obviously used to run El Capitan, a backup from that period would still have the old v3 folder which you could copy.

I do not see why you would want to copy all the emails again, clearly you have previously done this so why do you need to do this again? If only some 'new' emails need transferring then just export those rather than redoing the whole lot. Also this is what IMAP is for - that is using the same email account on more than one device and both devices then sync to the same copies on the server.

Are the folders you want to open in El Capitan Mail V3 your local "On My Mac" folders?

The easiest way to do this is with a third party app. Emailchemy $29.95

Has a demo you can try first. It will put a watermark on each email during the demo. You will have to run again to get "clean" emails.

http://www.weirdkid.com/products/emailchemy/

Use Emailchemy to export your Apple Mail folder in Sierra as regular .mbox files.

Select your Mail folder in your User's Library.

Select to Save as MBOX file ('standard mbox")

Revert to El Capitan with only your accounts added. Let it sync.

Under File > Import Mailboxes...

Select files in mbox format.

Your folders will come in to the local folders under Import. Drag out of Import to organize.

The proper way is to export your mail data as Apple mbox files rather than trying to import the files in the ~/Library/Mail folder. Sometimes it works but other times you get a strange folder structure.

An alternative if you have Time Machine is to restore from Time Machine. That would get all your nested folders.

Using Emailchemy gets all the nested folders.

Note: there are different kinds of .mbox files. An Apple .mbox file is not the same as a standard .mbox. In addition some apps are limited to a 2GB .mbox file and others have unlimited. Emailchemy has unlimited.

When you select to import data that is in the ~/Library/Mail folder you select Apple .mbox files.

The changes from V2 > V3 > V4 are a reflection of a different version of the SQLite database used by Mail. This gives us better performance. It's the upgrade process that is troublesome.

Apple's Mail application stores extensive information in SQLite, including e-mail addresses and message data. The database is located at /Users/account name/Library/Mail/Envelope Index

If you started with a clean Sierra Mail install and added IMAP accounts all messages and folders would download into the new index. However if you have POP accounts or store data under "On My Mac", you would need to export first as Apple .mbox files THEN import that data into your new clean Sierra Mail index.