Updated June 1st: First day postmarks:
Standard 4-bar FIRST DAY OF ISSUE
Digital Color Postmark:

from the Postal Bulletin May 27th:
On June 1, 2015, in Kansas City, MO, the U.S. Postal Service® will reissue the Yes, I Do two ounce rate mail-use stamp, (Non-denominated priced at 71 cents), in one design, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 589400).

The stamp will go on sale nationwide June 1, 2015.

The Weddings series Yes, I Do stamp, first issued in 2013, accommodates the heavier weight of an invitation, as well as other mailings such as oversized cards or small gifts that require extra postage. The stamp highlights the words “Yes, I Do” nestled in a bouquet of flowers in the shape of a heart on a white background. A similarly designed companion stamp, Where Dreams Blossom — a Forever® stamp first issued in 2013 — is also available for response cards, save-the-date notices, thank-you notes, and other correspondence. The stamp artwork was designed by Michael Osborne under the direction of Ethel Kessler. The words “two ounce” on this stamp indicate its usage value. Like a Forever® stamp, this stamp will always be valid for the rate printed on it. The initial price and value for this stamp is 71 cents.

How to Order the First-Day-of-Issue Postmark:
Customers have 60 days to obtain the first-day-of-Issue Postmark: by mail. They may purchase new stamps at their local Post Office, at The Postal Store® website at http://www.usps.com/shop, or by calling 800-STAMP-24. They should affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

71¢ Yes, I Do Stamp
Cancellation Services
8300 NE Underground Drive, Pillar 210
Kansas City, MO 64144-0001

After applying the first-day-of-Issue Postmark:, the Postal Service will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. For more than 50, customers have to pay five cents each. All orders must be postmarked by July 31, 2015.

There are five philatelic products for the Yes, I Do stamp issue:

• 589410, Digital Color Postmark Keepsake, $16.95.
• 589416, First-Day Cover, $1.15.
• 589421, Digital Color Postmark, $1.86.
• 589431, Stamp Deck Card, $0.95.
• 589432, Stamp Deck Card with Digital Color Postmark, $2.21.

Technical Specifications:

Issue: Yes, I Do Stamp
Item Number: 589400
Denomination & Type of Issue: Two Ounce Rate Non-Denominated, Mail-Use
Format: Pane of 20 (1 design)
Series: Weddings
Issue Date & City: June 1, 2015, Kansas City, MO 64108
Designer: Michael Osborne, Palo Alto, CA
Art Director: Ethel Kessler, Bethesda, MD
Typographer: Michael Osborne, Palo Alto, CA
Artist: Michael Osborne, Palo Alto, CA
Modeler: Joseph Sheeran
Manufacturing Process: Microprint, Offset
Printer: Ashton Potter (USA) Ltd. (APU)
Printed at: Williamsville, NY
Press Type: Muller A76
Stamps per Pane: 20
Print Quantity: 15 million stamps
Paper Type: Nonphosphored Type III, Block Tag applied
Adhesive Type: Pressure-sensitive
Processed at: Ashton Potter (USA) Ltd. (APU)
Colors: Black, Cyan, Magenta, Yellow, PMS 032 C Red
Stamp Orientation: Horizontal
Image Area (w x h): 1.42 x 0.84 in./36.07 x 21.34 mm
Overall Size (w x h): 1.56 x 0.98 in./39.62 x 24.89 mm
Full Pane Size (w x h): 7.24 x 5.95 in./183.90 x 151.13 mm
Press Sheet Size (w x h): n/a
Plate Size: 240 stamps per revolution
Plate Numbers: “P” followed by five (5) single digits
Marginal Markings: Front: Plate numbers in four corners of pane
Back: © 2012 USPS • USPS logo • Plate position diagram • Barcode (589400) in upper right and lower left corners of pane • Promotional text

From the USPS May 26th:
The Weddings series’ Yes, I Do stamp, issued in 2013, accommodates the heavier weight of an invitation, as well as other mailings such as oversized cards or small gifts that require extra postage. The stamp highlights the words “Yes, I Do” nestled in a bouquet of flowers in the shape of a heart on a white background. A similarly designed companion stamp, Where Dreams Blossom — a Forever stamp first issued in 2013 — is available for response cards, save-the-date notices, thank-you notes, and other correspondence. The stamp artwork was designed by Michael Osborne of Palo Alto, CA, under the direction of Ethel Kessler of Bethesda, MD. The words “TWO OUNCE” on this stamp indicate its usage value. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The initial price and value for this stamp is 71 cents effective May 31.

From the USPS May 18th:
The Weddings series’s Yes, I Do stamp, first issued in 2013, accommodates the heavier weight of an invitation, as well as other mailings such as oversized cards or small gifts that require extra postage. The stamp highlights the words “Yes, I Do” nestled in a bouquet of flowers in the shape of a heart on a white background. A similarly designed companion stamp, Where Dreams Blossom—a Forever stamp first issued in 2013—is available for response cards, save-the-date notices, thank-you notes, and other correspondence. The stamp artwork was designed by Michael Osborne under the direction of Ethel Kessler. The words “two ounce” on this stamp indicate its usage value. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The initial price and value for this stamp is 71 cents.

The first day of issue is June 1, without a ceremony. The city is Kansas City (Stamp Fulfillment Services).