Engagesmart (ESMT) 8-K Other Events

Exhibit 5.1

	1271 Avenue of the Americas
	New York, New York 10020-1401
	Tel: +1.212.906.1200 Fax: +1.212.751.4864
	www.lw.com
	FIRM / AFFILIATE OFFICES
	Austin	Milan
	Beijing	Munich
	Boston	New York
	Brussels	Orange County
March 1, 2023	Century City	Paris
	Chicago	Riyadh
	Dubai	San Diego
	Düsseldorf	San Francisco
	Frankfurt	Seoul
EngageSmart, Inc.	Hamburg	Shanghai
30 Braintree Hill Office Park, Suite 101	Hong Kong	Silicon Valley
Braintree, Massachusetts 02184	Houston	Singapore
	London	Tel Aviv
	Los Angeles	Tokyo
	Madrid	Washington, D.C.

Re: Registration Statement on Form S-3 (No. 333-270090)

Up to 9,200,000 shares of Common Stock $0.001 par value per share

To the addressee set forth above:

We have acted as special counsel to EngageSmart, Inc., a Delaware corporation (the “Company”), in connection with the proposed sale of up to 9,200,000 shares (the “Shares”) of the Company’s common stock, $0.001 par value per share (“Common Stock”), by the selling stockholders named in the Preliminary Prospectus (as defined below) and the Prospectus (as defined below), including up to 1,200,000 shares of Common Stock that may be sold by certain of the selling stockholders upon exercise of the underwriters’ option to purchase additional shares. The Shares are included in a registration statement on Form S-3 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on February 28, 2023 (Registration No. 333-270090) (as amended, the “Registration Statement”), and are being offered pursuant to a base prospectus dated February 28, 2023 (the “Base Prospectus”), a preliminary prospectus supplement dated February 28, 2023 filed with the Commission pursuant to Rule 424(b) under the Act (together with the Base Prospectus, the “Preliminary Prospectus”) and a prospectus supplement dated February 28, 2023 filed with the Commission pursuant to Rule 424(b) under the Act (together with the Base Prospectus, the “Prospectus”). The Shares are being sold pursuant to an underwriting agreement dated February 28, 2023 among Goldman Sachs & Co. LLC and J.P. Morgan Securities LLC, as representatives of the several underwriters named therein, the selling stockholders named therein and the Company (the “Underwriting Agreement”).

This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement, the Preliminary Prospectus or the Prospectus, other than as expressly stated herein with respect to the issue of the Shares.

March 1, 2023

Page 2

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware, and we express no opinion with respect to any other laws.

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, the Shares have been duly authorized by all necessary corporate action of the Company and are validly issued, fully paid and nonassessable.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Company’s Current Report on Form 8-K filed with the Commission on March 1, 2023 and to the reference to our firm contained in the Prospectus under the heading “Legal Matters.” In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.

Sincerely,

/s/ LATHAM & WATKINS LLP