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Iamgold Updates Diamond Drilling Results ON Its Advanced Boto Exploration Project, Senegal

Drill Results

NEWS RELEASE

TSX: IMG NYSE: IAG

IAMGOLD UPDATES DIAMOND DRILLING RESULTS ON ITS ADVANCED BOTO

EXPLORATION PROJECT, SENEGAL

Toronto, Ontario, May 31, 2017 – IAMGOLD Corporation (“IAMGOLD” or the “Company”) today announced

additional drilling results from its 100% owned Boto Gold Project in eastern Senegal, West Africa. The

reported assay results are from the remaining twenty -two diamond drill holes, totaling 2,842 metres,

completed at the Malikoundi deposit and Malikoundi North extension. The Company’s ongoing drilling

program had resumed in the fourth quarter of 2016 after seasonal rains, and continued into the first quarter of

2017.

The assay results are provided in Tables 1 and 2 and include the following highlights:

Malikoundi Deposit (Deepened Holes):

 Drill Hole DBDD-2201: 37 metres grading 1.83 g/t gold

and 19 metres grading 3.28 g/t gold

 Drill Hole DBDD-2261: 42 metres grading 1.26 g/t gold

 Drill Hole DBDD-2266: 77 metres grading 4.35 g/t gold

Includes: 9 metres grading 11.76 g/t gold

Malikoundi North Extension:

 Drill Hole DBDD-2321: 14 metres grading 1.64 g/t gold

 Drill Hole DBDD-2322: 22 metres grading 1.79 g/t gold

Craig MacDougall, Senior Vice President, Exploration for IAMGOLD , stated, "With the last round of drilling

results now in hand from our drilling program at the Malikoundi deposit, we are working to update the resource

model for use in our ongoing technical evaluation of the project. Our drilling activities are now focused on

targeting possible resource expansions at the Boto 5 and Boto 6 deposits.”

BOTO PROJECT, SENEGAL

The Boto project comprises 236 square kilometres of exploration licenses located in eastern Senegal along

the Senegal-Mali border. The geological setting of the project area is similar to the prolific Sadiola and Loulo

gold districts in adjacent Mali, being underlain by h ighly prospective, Birimian-aged metasedimentary, volcanic

and intrusive rocks along a seven-kilometre strike length of the Senegal-Mali Shear Zone.

As of December 31, 2016, the project hosts an indicated resource of 27.7 million tonnes averaging 1.8 gram s

of gold per tonne for 1.56 million ounces and an inferred resource of 2.9 million tonnes averaging 1.3 grams of

gold per tonne for 125,000 ounces (see news release regarding reserves and resources dated February 22,

2017).

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Next Steps

The drilling results from Malikoundi will be incorporated into an updated resource model for the Boto project.

Diamond drilling activities continue on the property t argeting additional mineral resources along known

mineralized trends associated with the Boto 5 and Boto 4-6 deposits.

Technical Information and Quality Control Notes

Boto Project, Senegal:

The Boto drilling results contained in this news release have been prepared in accordance with National

Instrument 43-101 Standards of Disclosure for Mineral Projects. The sampling of, and assay data from, drill

core is monitored through the implementation of a qua lity assurance - quality control (QA -QC) program

designed to follow industry best practice. Drill core (HQ and NQ size) samples are selected by the IAMGOLD

geologists and sawn in half with a diamond saw at the project site. Half of the core is retained at the site for

reference purposes. Sample intervals are generally 1 metre in length. Samples are prepared at the Veritas

Preparation Laboratory in Bamako, Mali and analyzed using a standard fire assay with a 50 gram charge with

an Atomic Absorption (AA) finish at the Veritas Analytical Laboratory in Abidjan, Ivory Coast.

Qualified Persons

The information in this news release was prepared under the supervision of, and reviewed and verified by,

Craig MacDougall, P.Geo., Senior Vice President, Exploration for IAMGOLD. Mr. MacDougall is a Qualified

Person as defined by National Instrument 43-101.

Forward Looking Statement

This news release contains forward-looking statements. All statements, other than of historical fact, that

address activities, events or developments that the Company believes, expects or anticipates will or may

occur in the future (including, without limitation, statements regarding expected, estimated or planned gold

production, cash costs, margin expansion, capital expenditures and exploration expenditures and statements

regarding the estimation of mineral resources, exploration results, potential mineralization, potential mineral

resources and mineral reserves) are forward-looking statements. Forward-looking statements are generally

identifiable by use of the words “will”, “continue”, “expect”, “estimate”, “intend”, “to have’, “plan” or “project” or

the negative of these words or other variations on these words or comparable terminology. Forward -looking

statements are subject to a number of risks and uncertainties, many of which are beyond the Company’s

ability to control or predict, that may cause the actual results of the Company to differ materially from those

discussed in the forward-looking statements. Factors that could cause actual results or events to differ

materially from current expectations include, among other things, without limitation, failure to meet expected,

estimated or planned gold production, cash costs, margin expansion, capital expenditures and exploration

expenditures and failure to establish estimated mineral resources, the possibility that future exploration results

will not be consistent with the Company's expectations, changes in world gold marke ts and other risks

disclosed in IAMGOLD’s most recent Form 40-F/Annual Information Form on file with the United States

Securities and Exchange Commission and Canadian provincial securities regulatory authorities. Any forward -

looking statement speaks only as of the date on which it is made and, except as may be required by

applicable securities laws, the Company disclaims any intent or obligation to update any forward -looking

statement.

About IAMGOLD

IAMGOLD ( www.iamgold.com) is a mid -tier mining company with four operating gold mines on three

continents. A solid base of strategic assets in North and South America an d West Africa is complemented by

development and exploration projects and continued assessment of accretive acquisition opportunities.

IAMGOLD is in a strong financial position with extensive management and operational expertise.

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For further information please contact:

Ken Chernin, VP Investor Relations, IAMGOLD Corporation

Tel: (416) 360-4743 Mobile: (416) 388-6883

Laura Young, Director, Investor Relations, IAMGOLD Corporation

Tel: (416) 933-4952 Mobile: (416) 670-3815

Shae Frosst, Investor Relations Associate, IAMGOLD Corporation

Tel: (416) 933-4738 Mobile: (647) 967-9942

Toll-free: 1-888-464-9999 [email protected]

Please note:

This entire news release may be accessed via fax, e -mail, IAMGOLD's website at www.iamgold.com and through CNW Group’s website

at www.newswire.ca. All material information on IAMGOLD can be found at www.sedar.com or at www.sec.gov.

Si vous désirez obtenir la version française de ce communiqué, veuillez consulter le http://www.iamgold.com/French/accueil/default.aspx.

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Notes:

1. Drill hole intercepts are calculated using a minimum down-hole length of 2 meters, a cut-off grade of 0.5 g/t gold, a global assay cap of

25 g/t gold and may include up to 5 metres of internal dilution.

2. The true widths of intersections are interpreted to approximate the reported downhole lengths.

Notes:

1. Drill hole intercepts are calculated using a minimum down-hole length of 2 meters, a cut-off grade of 0.5 g/t gold, a global assay cap of

25 g/t gold and may include up to 5 metres of internal dilution.

2. The true widths of intersections are interpreted to approximate the reported downhole lengths.

3. *- previously reported footwall intercept (see new releases dated October 20, 2014;February 3, 2015, April 23, 2015 and July 20, 2015)

Hole# AZ DIP EOH From To Length Grade

Easting Northing Elevation (degrees) (degrees) (m) (m) (m) (m) (g/t Au)

2313 241964 1379263 165 90 -60 225 81 85 4 1,12

116 118 2 0,73

2314 242030 1379121 165 90 -60 215 63 65 2 0,65

2315 242128 1379248 164 90 -60 125 No significant intersection

2316 242159 1378899 162 115 -60 60 No significant intersection

2321 241943 1380065 163 115 -60 99 71 85 14 1,64

2322 241986 1380047 163 115 -60 45 13 35 22 1,79

2323 241903 1380302 162 115 -60 150 69 72 3 0,79

122 133 11 1,10

2324 241905 1380410 160 115 -60 150 127 131 4 1,48

2325 241946 1380501 159 115 -60 102 44 46 2 0,74

83 85 2 3,38

2326 242001 1380532 158 115 -60 42 14 16 2 0,84

2327 241957 1380674 131 122 -60 99 No significant intersection

2328 242004 1380652 133 115 -60 45 No significant intersection

2329 241894 1380251 162 115 -60 170 No significant intersection

2330 241912 1380464 159 115 -60 160 117 129 12 1,47

2331 241896 1380195 162 115 -60 170 126 140 14 0,80

2332 242000 1379683 165 115 -60 60 44 48 4 0,52

2333 241986 1379822 164 115 -60 60 44 49 5 0,59

2334 241955 1379704 165 115 -60 108 93 95 2 1,99

2335 241941 1379842 164 115 -60 108 86 90 4 3,29

2336 241983 1379942 164 115 -60 61 26 40 14 0,99

2338 241938 1379963 164 115 -60 108 71 84 13 0,84

Total 2362

Table 1: Boto Project Drilling Results – Malikoundi and Malikoundi North Deposit

UTM (WGS84Zone29N)

Hole# AZ DIP EOH From To Length Grade

Easting Northing Elevation (degrees) (degrees) (m) (m) (m) (m) (g/t Au)

2201 Ext 241728 1379267 166 116 -60 470 375 412 37 1,83

including 405 407 2 15,37

420 439 19 3,28

2204* 241770 1379357 166 116 -60 350 318 350 32 1,67

2204 Ext 241770 1379357 166 116 -60 410 318 354 36 1,58

2217 Ext 241726 1379204 166 115 -60 500 407 411 4 2,95

428 433 5 0,80

478 481 3 1,26

2225 Ext 241776 1379295 166 116 -60 420 398 411 13 2,01

2259* 241633 1379366 166 115 -60 481 415 480 65 1,57

2259 Ext 241633 1379366 166 115 -60 570 415 492 77 1,48

503 510 7 1,74

522 527 5 5,54

533 567 34 1,34

2261* 241727 1379323 166 115 -60 417 403 415 12 2,07

2261 Ext 241727 1379323 166 115 -60 465 403 445 42 1,26

2266* 241639 1379254 166 115 -60 465 432 465 33 4,28

2266 Ext 241639 1379254 166 115 -60 525 432 509 77 4,35

including 469 478 9 11,76

including 483 485 2 9,77

523 525 2 4,49

Total 480

Table 2: Boto Project Drilling Results – Deepened Drill Holes (Ext), Malikoundi Deposit

UTM (WGS84Zone29N)

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