It will come by ordinary USPS mail. You can check your case status with your receipt number at www.uscis.gov to find more specific information about when it was produced by USCIS, when it was deliver to USPS, and when it was delivered to your address. Checking your case status on uscis.gov will also provide you with a USPS tracking number that you can use to follow up with them if you have a problem with delivery. Congratulations!
The information offered is general in nature and not meant to be relied upon as legal advice. No client-attorney relationship is created through this information. Please consult an attorney prior to making legal decisions.
They send it by regular mail. If you do not get it within 30 days after the approval, you should make an infoPass appointment to report it and get a new I-551 stamp in your passport, if needed.
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If you contact customer service, you can get a tracking number as all cards being sent by USCIS are typically sent priority mail with delivery confirmation now. If you are concerned, contact customer service for the tracking number and confirm the name/address it was sent to. If your case status shows card production has been ordered, you should expect it in the mail in the next two weeks.
This answer is only for general information purposes. It does not establish an attorney-client relationship. The answer I gave is based only on the facts that you have presented in your question and might change if the facts are different.